feat: add persistent parameter shorthand

[kichristensen]

What does this change

Adds a persistent: true shorthand on parameter definitions so a value provided at install is automatically remembered for subsequent upgrade and uninstall runs — without manually wiring outputs and parameter sources.

schemaVersion: 1.2.0

parameters:
  - name: resource-group
    type: string
    persistent: true

Enable the feature:

export PORTER_EXPERIMENTAL=persistent-parameters

At manifest validation time, persistent: true expands into:

• a file destination at /cnab/app/<name>
• source.output: <name>
• an explicit applyTo list covering all declared actions (including install)
• a matching output definition (unless one already exists)

No changes to the CNAB adapter are required — after expansion the param is identical to the longhand.

What issue does it fix

Closes #1889

Notes for the reviewer

• Schema version 1.2.0 is required; gated behind the persistent-parameters experimental feature flag (same pattern as DepsV2 / 1.1.0)
• persistent: true hard-errors when combined with source, path/env, or applyTo
• applyTo is set explicitly (including install) to prevent exemptFromInstall() from silently dropping install from the list

Checklist

• Did you write tests?
• Did you write documentation?
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
• If this is your first pull request, please add your name to the bottom of our Contributors list. Thank you for making Porter better! 🙇‍♀️