feat(env): add github-actions output format

[jongio]

Adds a --format github-actions option to azd app env so a service's resolved environment can be written straight into a workflow's $GITHUB_ENV file.

Why

Getting an app's resolved config into a GitHub Actions job today means hand-writing echo "KEY=value" >> $GITHUB_ENV lines or post-processing the dotenv output, and that breaks the moment a value spans multiple lines (PEM keys, certs, JSON blobs). GitHub Actions has a specific line format for that; this teaches env to emit it directly.

What

• New format value github-actions for --format.
• Single-line values render as KEY=value (no quoting, since the file is not shell-parsed).
• Multiline values render with the KEY<<DELIM heredoc form. The delimiter is random (crypto/rand) and checked against the value so it can never collide with the content, which also closes the usual env-injection hole.
• Works with --all (per-service # name headers are dropped so the stream stays valid) and with --write.
• Masking still applies by default; use --no-mask when you actually want the values in the file.

Usage

azd app env api --format github-actions --no-mask >> $GITHUB_ENV

Tests

• resolveEnvFormat accepts github-actions (case-insensitive) and its error text lists it.
• formatGitHubEnv: sorted single-line output, no shell quoting of special characters, multiline heredoc round-trips the exact value with a non-colliding delimiter, masking applies first.
• githubEnvDelimiter: never a substring of the value, randomized between calls.

Closes #495

[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.76%. Comparing base (dd00a47) to head (435eceb).

Files with missing lines	Patch %	Lines
cli/src/cmd/app/commands/env.go	60.00%	15 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #500      +/-   ##
==========================================
- Coverage   60.77%   60.76%   -0.01%     
==========================================
  Files         223      223              
  Lines       28527    28574      +47     
==========================================
+ Hits        17337    17364      +27     
- Misses      10010    10025      +15     
- Partials     1180     1185       +5     

Flag	Coverage Δ
unittests	60.76% <60.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
cli/src/cmd/app/commands/env.go	79.33% <60.00%> (-3.26%)	⬇️

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[github-actions]

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One-Line Install (Recommended)

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Uninstall

When you're done testing:

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Bash (macOS/Linux):

curl -fsSL https://raw.githubusercontent.com/jongio/azd-app/main/cli/scripts/uninstall-pr.sh | bash -s 500

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Build Info:

• Version: 0.19.5-pr500
• Commit: 435eceb
• Release: View pre-release

What to Test:
Please review the PR description and test the changes described there.