Add new columns to external status checks table

Artur Fedorovrequested to merge
433035-status-checks-add-column-secret into master

What does this MR do and why?

New column to store HMAC secret and initialisation vector. These secrets will be used for authentication of external status checks.

This merge request updates the database schema for GitLab. It adds new columns to various tables, including encrypted_shared_secret and encrypted_shared_secret_iv to the external_status_checks table, and makes several other changes to table structures and constraints. These modifications enhance the platform's functionality and data management capabilities.

Parent issue: #433035 (closed)

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Related to #433035 (closed)

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