Github Action Added to Block PRs from fork/main branch

[varshith257]

Which problem is this PR solving?

• Resolves https://github.com/jaegertracing/jaeger/issues/5271

Description of the changes

• Added the github actions file that check the PR is from main branch of fork and blocks it.

How was this change tested?

• Will be tested

Checklist

• [x] I have read https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
• [x] I have signed all commits
• [x] I have added unit tests for the new functionality
• [x] I have run lint and test steps successfully
  • for jaeger: make lint test
  • for jaeger-ui: yarn lint and yarn test

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[varshith257]

@yurishkuro PTAL

[yurishkuro]

Thanks!