[mgmt] eventgrid release

[kazrael2119]

https://github.com/Azure/sdk-release-request/issues/5894

Pull Request Overview

This PR prepares the eventgrid release by updating documentation links, changelog entries, and sample files to reference stable API versions and new subscription IDs where applicable.

• Updated API reference link in README.md
• Expanded and finalized changelog entries in CHANGELOG.md
• Updated sample files to reference the stable API and new subscription IDs, and made a minor adjustment in the core-rest-pipeline API definition

Reviewed Changes

Copilot reviewed 577 out of 577 changed files in this pull request and generated no comments.

File	Description
sdk/eventgrid/arm-eventgrid/README.md	Updated API reference URL and removed outdated setup instructions.
sdk/eventgrid/arm-eventgrid/CHANGELOG.md	Updated changelog entries, including new operation groups and interface additions.
sdk/core/core-rest-pipeline/review/core-rest-pipeline.api.md	Replaced the anonymous symbol with [custom] and added a warning comment regarding its export.
sdk/eventgrid/arm-eventgrid/samples-dev/*.ts	Updated sample files to reference the stable API (2025-02-15) and standardized subscription ID values across samples.

Comments suppressed due to low confidence (1)

sdk/core/core-rest-pipeline/review/core-rest-pipeline.api.md:379

• Ensure that 'custom' is defined or imported as a symbol, and that it is properly exported from the entry point to avoid potential runtime issues.

[custom]: () => string;