Add security policy bypass push option

What does this MR do and why?

As a part of BE: Extend policy bypass option to include user... (#549797 - closed), we want to allow users/groups to bypass the approvals and branch protection enforced through security policy. This can be done at 2 levels:

• Merge Request: An user/group can bypass the approvals by providing a reason from the MR UI. The reason will be persisted in approval_policy_merge_request_bypass_events introduced with !199151 (merged)
• Branch Push: An user can push to a branch with push protection (protected branch and branch protection from MR approval policy) through a git push options (something like --push-option security_policy.bypass_reason='reason')

This MR adds boilerplate changes for the new push option for security policy with bypass reason. The push option will be processed in the second MR

• 1️⃣ 👉 Add security policy bypass push option (!200025 - merged)
• 2️⃣ Extend policy bypass checker with users, roles ... (!201001 - merged)

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Related to #549797 (closed)