added sigterm telemetry event api

[gireesh-devtron]

Description

added an api endpoint in telemetry client to send sigterm event to posthog. This endpoint is used in prestop hook in orchestrator container to send sigterm event before stoping the container.

Fixes # (issue)

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

-> This api endpoint has been tested locally and able to send sigterm event from demo1 client. -> able to send payload

• [x] Test case A
• [ ] Test case B

Checklist:

• [x] The title of the PR states what changed and the related issues number (used for the release note).
• [ ] Does this PR require documentation updates?
• [ ] I've updated documentation as required by this PR.
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have tested it for all user roles
• [ ] I have added all the required unit/api test cases

[gireesh-devtron]

@manish-agrawal-ai please review this PR