Dev Container lock file and Dependabot configuration for devcontainers

[brooke-hamilton]

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Description

Addition of a devcontainer lock file (.devcontainer/devcontainer-lock.json) to pin devcontainer feature versions with integrity hashes, and a new Dependabot configuration entry in .github/dependabot.yml for automated weekly updates of devcontainer features on the edge branch.

Changes

• .devcontainer/devcontainer-lock.json (new): Pins devcontainer features (git, go, hugo, node) to specific versions with SHA-256 integrity hashes for reproducible builds.
• .github/dependabot.yml (modified): Adds a devcontainers package ecosystem entry targeting the edge branch with a weekly update schedule.

Issue reference

N/A — Proactive improvement to pin devcontainer feature versions and enable automated dependency updates.

[DariuszPorowski]

idea: How about keeping version of features explicite in devcontainer.json to be aligned with lock file? like here: https://github.com/radius-project/wellknown/blob/87d878457e7740aa9073f9373025d561986a46b6/.devcontainer/devcontainer.json#L9 Dependabot handles this nicely and versions always match 1:1 between files: https://github.com/radius-project/wellknown/pull/48/changes

[brooke-hamilton]

@copilot implement suggestion in comment #1776 (review)

[Copilot]

@brooke-hamilton I've opened a new pull request, #1781, to work on those changes. Once the pull request is ready, I'll request review from you.

[brooke-hamilton]

idea: How about keeping version of features explicite in devcontainer.json to be aligned with lock file? like here: https://github.com/radius-project/wellknown/blob/87d878457e7740aa9073f9373025d561986a46b6/.devcontainer/devcontainer.json#L9 Dependabot handles this nicely and versions always match 1:1 between files: https://github.com/radius-project/wellknown/pull/48/changes

Good idea. Implemented.