Update RuleForm inputs to use GlFormInput and GlFormGroup

What does this MR do?

This MR replaces the RuleForm's inputs with GlFormInput and GlFormGroup. Previously this was using the classes of these components but not actually using them, which made the view particularly convoluted and repetitive. Using them directly, retains the same style but also makes the view simpler and means this form will be kept up-to-date with future GitLab UI changes.

This does not change any of the visual aspects of the form.

This is a two-part refactor:

Step	MR
Refactor the validation	!56961 (merged)
Refactor to use GlFormInput/GlFormGroup	👉 You are here

Screenshots (strongly suggested)

Form	With validation errors

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because this is a refactor and makes no visual changes. The existing inputs used the same classes a those from the GitLab UI components
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

1. Open a project and go to project settings, then open the Merge request approvals section
2. Check that adding and editing approval rules works as expected

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] 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 #323729 (closed)