Add maximum for approvals_required

What does this MR do?

Ensure ApprovalRule's approvals_required is capped at maximum 100.

During data migration, it is discovered some were set to very high value, which the new 2 byte field can't contain. We cap this so the migration can still run.

What are the relevant issue numbers?

#9263 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder

Closes #9263 (closed)