Group Settings Default initial branch h4 expand

What does this MR do?

This MR adds classes settings-title, js-settings-toggle and js-settings-toggle-trigger-only to the h4 header Group Settings / Repository Settings / Default initial branch name. This enables the expand/collapse behavior on mouse-click / tap for the h4 header.

Related to issue #334655 (closed) reported by @mle.

Screenshots (strongly suggested)

Current behavior: no on-click / on-tap expand/collapse

Behavior after applying this MR: on-click / on-tap expand/collapse

(Copied from my first related MR !55228 (merged) for simplicity. I will update the screenshots and video 😸 )

Screen_Recording_2021-08-25_at_08.57.55

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
  • Apple Safari 13.1.2 (13609.3.5.1.5)
  • Chromium Version 90.0.4409.0
  • Google Chrome 88.0.4324.146
  • Microsoft Edge 88.0.705.56
  • Mozilla Firefox 84.0.2
• 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