Docs: Updated GitHub data source docs

[lwandz13]

Overhaul the GitHub data source plugin documentation to align with Grafana's official documentation standards. This restructures fragmented pages into a flat file layout, adds missing content, verifies accuracy against the codebase, and improves overall clarity and flow.

Structure changes

Consolidated 12 files across 5 directories into 7 flat files under docs/sources/:

• setup/* (5 files) → configure.md
• query/_index.md → query-editor.md
• variables-and-macros/* (3 files) → template-variables.md
• annotations/_index.md → annotations.md
• troubleshoot/_index.md → troubleshooting.md
• sample-dashboards/_index.md content merged into _index.md

Created new alerting.md — The plugin supports alerting (plugin.json: "alerting": true) but had no documentation for it.

Content additions

• _index.md: Added Requirements, Common use cases (7 engineering scenarios), expanded Pre-built dashboards section with panel descriptions.
• configure.md: Added Security best practices section, Terraform provisioning examples (PAT, GitHub App, Enterprise Server), PDC "Manage" link, improved Save & test guidance. Elevated Code scanning permissions to apply to both PATs and GitHub Apps.
• query-editor.md: Added documentation for Code scanning and Pull request reviews query types. Added 7 new sample queries across Issues, Pull Requests, Pull Request Reviews, and Workflow Runs. Fixed response field inaccuracies verified against Go source (star_count typo, missing author_email, state, milestone, is_fork, merged_by_email, merged_by_company, updated_at, open_time, labels).
• alerting.md: New page covering supported query types, step-by-step alert rule creation, 3 example alert configurations, caching considerations, and template annotations/labels.
• annotations.md: Added 3 use case examples (releases on performance dashboards, deployment tracking, merged PRs alongside commits).
• template-variables.md: Added Before you begin, Supported variable types, multi-variable dashboard walkthrough (owner → repo → labels chaining), improved macro descriptions (prefix → qualifier terminology).
• troubleshooting.md: Expanded from a brief page to comprehensive coverage: auth errors (PAT, GitHub App, private repos), connection errors (Enterprise Server, network), query errors (no data, result limits with source attribution, rate limiting), code scanning errors, debug logging, and escalation guidance.

[cla-assistant]

All committers have signed the CLA.

[Copilot]

Pull request overview

Overhauls and consolidates the GitHub data source plugin documentation into a flatter, Grafana-standard page structure under docs/sources/, adding missing feature coverage (notably alerting) and expanding guidance for configuration, querying, variables, and troubleshooting.

Changes:

• Consolidates prior multi-directory docs into a smaller set of top-level docs pages with aliases for old routes.
• Adds/expands documentation for query editor behavior, template variables/macros, alerting, annotations, and troubleshooting.
• Updates the docs landing page content (requirements, capabilities, use cases, dashboards, caching, and resources).

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
docs/sources/_index.md	Updates landing page content, adds aliases, requirements, capabilities, use cases, dashboards, caching.
docs/sources/configure.md	New consolidated configuration/auth/provisioning (YAML + Terraform) guide.
docs/sources/query-editor.md	New consolidated query editor reference across query types and response fields.
docs/sources/template-variables.md	New consolidated template variables + macros documentation with walkthrough examples.
docs/sources/annotations.md	New consolidated annotations guide with use-case examples.
docs/sources/alerting.md	New alerting page describing supported patterns and examples.
docs/sources/troubleshooting.md	New expanded troubleshooting guide for auth/connection/query/code scanning/debugging.
docs/sources/query/_index.md	Removes old query docs (replaced by query-editor.md + alias).
docs/sources/setup/_index.md	Removes old setup index (replaced by configure.md + alias).
docs/sources/setup/installation.md	Removes old installation page (covered by configure.md).
docs/sources/setup/token.md	Removes old token page (covered by configure.md).
docs/sources/setup/datasource.md	Removes old datasource config page (covered by configure.md).
docs/sources/setup/provisioning.md	Removes old provisioning page (covered by configure.md).
docs/sources/variables-and-macros/_index.md	Removes old variables/macros index (replaced by template-variables.md + aliases).
docs/sources/variables-and-macros/variables.md	Removes old variables page (replaced by template-variables.md).
docs/sources/variables-and-macros/macros.md	Removes old macros page (replaced by template-variables.md).
docs/sources/annotations/_index.md	Removes old annotations page (replaced by annotations.md + alias).
docs/sources/troubleshoot/_index.md	Removes old troubleshooting page (replaced by troubleshooting.md + alias).
docs/sources/sample-dashboards/_index.md	Removes old sample dashboards page (content merged; alias added on landing page).
.vscode/settings.json	Adds a VS Code workspace setting.

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