Rename require_password_to_approve

This setting is no longer just for passwords, but also being used to ask the user to re-authenticate with SAML if they have it setup, so we need to make the naming reflect a general re-authentication.

Rename merge_request_approval_setting for password require_password_to_approve => require_reauthentication_to_approve

• rename DB
  • Take !52032 (merged)+s into account
• update API for MergeRequestApprovalSettings to accept require_reauthentication_to_approve besides previous parameter.
  • Make sure the value is mirrored between both columns in the interim until we fully remove require_password_to_approve to keep them in sync.
• add migration to sync previous setting to require_reauthentication_to_approve
  • migration for project_settings => Rework !155652 (closed) to a batched background migration
  • migration for group_merge_request_approval_settings
• rename occurrences in frontend => Rename references to require_password_to_approv... (#468866) • SAM FIGUEROA • 19.0
• rename occurrences in backend => Rename references to require_password_to_approv... (#468866) • SAM FIGUEROA • 19.0
• update documentation

Refs: !130204 (merged)