Block merge if code coverage on NEW code is < 70%

We currently have a code coverage reporter for our go code.
However there are a few tweaks we could make.

On all GO repos:
1. Code coverage is for all code, not a delta against develop. This means a PR could have zero coverage but overall levels could remain high giving false confidence.
2. Code coverage levels do not currently block a PR from merging. This should be automated and enforced

See https://github.com/0chain/blobber/issues/151

Look at the existing code coverage reporter setup in the Go repositories. Examine the linked issue #151 in the blobber repo for context. The task involves modifying CI/CD to compute coverage delta against the develop branch and enforce a 70% threshold on new code to block merges. Start by understanding the current coverage tool (likely go test with cover) and the CI configuration (e.g., GitHub Actions).

Vom Indexierungsmodell aus dem Issue-Text verfasst.