Create an agentic workflow that automatically applies documentation labels to PRs

Implement an agentic workflow that automatically identifies pull requests requiring updates to public-facing documentation (https://learn.microsoft.com/en-us/azure/azure-resource-manager/bicep/) and applies the appropriate `Docs Needed` or `Docs Not Needed` label.

Changes that require documentation updates usually include:

- New linter rules.
- New language constructs (keywords, syntax, decorators, functions, operators, etc.).
- GA of experimental features.
- New language features or capabilities, even if they don't introduce new syntax (for example, new module capabilities or deployment behaviors).
- Changes to diagnostics or compiler behavior that affect how users write or troubleshoot Bicep code.
- Changes to configuration files or settings that users are expected to author (for example, `bicepconfig.json`).

No file, test, or workflow entry point is named. Start by reviewing the repository's existing pull-request labeling workflows and the `Docs Needed` and `Docs Not Needed` labels, then map the listed documentation-impact criteria to the desired classification behavior and verify the workflow on representative pull requests.

Written by the indexing model from the issue text.