SDK generation agentic flow: Use integrity filter for workflow security

Update SDK generation agentic flow to add integrity filtering front matter in the gh-aw workflow. Also update the doc to refer this as important point to do in the gh-aw for security reasons. Doc link: https://github.com/Azure/azure-sdk-tools/blob/main/doc/github_agent_workflow.md

Refer [integrity-filtering](https://github.github.com/gh-aw/reference/integrity/) for more info.

//cc: @weshaggard