Add a locked state to approval settings checkbox

What does this MR do?

This MR adds optional locked & lockedText properties to the approval settings checkbox as described in #335962 (closed).

When a locked is true, the component should:

• Disable the checkbox input.
• Display a lock icon.
• The lock icon should have a popover with the lockedText message.

This will be used by the ApprovalSettings component to lock settings for a project #332548 (closed) or group #332549 (closed).

Screenshots or Screencasts (strongly suggested)

Before	After	Design

Local testing & setup

1. You need a GitLab Ultimate license.
2. Enable the feature flag: echo "Feature.enable(:group_merge_request_approval_settings_feature_flag)" | rails c
3. View the Merge request approvals in [GDK_HOST]/groups/gitlab-org/-/edit.
4. Open vue dev tools and edit the lockedBy value of any ApprovalSettingsCheckbox component.
5. Verify that it does what is outlined in the MR's description.

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?) No visual change
• I have added/updated documentation, or it's not needed. (Is documentation required?) No visual change
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #335962 (closed)