Fix repository clone panel for wikis

What does this MR do?

Part of #207869 (closed), extracted from !45892 (merged).

This fixes a small bug with wikis where the dropdown label wasn't updated correctly when switching the protocol.

Since we want to reuse this for group wikis, this also generalizes the code a bit by:

• Moving the JS initializer into its own file.
• Moving the wiki specs for the clone panel into shared examples, and extending it to verify the dropdown switching behaviour.
• Using container rather than project in variable names.
• Using repositories rather than project code in UI strings.
• Renaming enabled_project_button to enabled_protocol_button, to make the intent clearer.

This clone panel also uses an outdated design, I opened #281830 (closed) as a follow-up to maybe switch to the new Vue clone button.

Screenshots (strongly suggested)

Description	Screenshot
Default clone dropdown
Clone field when only one protocol is available

(note that GDK shows HTTP, on production we'll get HTTPS)

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
• [-] 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