[WIP] [Don't merge]Adding API spec for bloack service

[kumarashit]

What type of PR is this?

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kind new feature

/kind bug fix /kind cleanup /kind revert change /kind design /kind documentation /kind enhancement

What this PR does / why we need it: Adding Block API spec Which issue(s) this PR fixes:

Fixes #

Test Report Added?:

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Test Report:

Special notes for your reviewer: