Automated release plan and SDK release notification

Release plans are automatically generated when a spec PR merges to main(both mgmt and data plane) and SDK pull request is auto generated(only mgmt plane) and auto triggered the release pipeline for management plane.

We need to send automated email notification to inform
- [x] when a release plan is created (Audience: spec author, spec code owner and azsdk engagement exp support (azsdkexp@microsoft.com))
- [ ] when SDK PR is auto generated (Audience: release plan owner, SDK code owner, SDK team(management and data plane) and azsdk engagement exp support(azsdkexp@microsoft.com))
- [ ] when SDK release pipeline is ready to approve (Audience: release plan owner, SDK code owner, SDK team(management and data plane) and azsdk engagement exp support(azsdkexp@microsoft.com))
- [ ] scheduled failed SDK generation failure notification (Audience: azsdk engagement exp support(azsdkexp@microsoft.com))

SDK team alias for management plane release plans: [sdkowners@microsoft.com](mailto:sdkowners@microsoft.com)