Remove unused group/project parameters from runner instructions modal

What does this MR do?

Remove unused group/project parameters from runner instructions modal

This MR cleans up unused parameters from the runner install instructions.

As runner installation instructions no longer depend on the user, project ID, or group ID this can be safely removed.

UX improvements

Additional UX improvements have been added:

• Reduce spacing between modal elements (from 1rem to 0.5rem) to keep the modal shorter in the screen, preventing some scrolling in smaller screens, or when instructions are long.
• Added loading icon when instructions are loading, the loading icon is next to the architecture dropdown.
• Used checkmarks in architecture dropdowns (using is-check-item), as well as "selected" buttons for the platform.
• Improved the copy of the instructions, by removing a dangling Method title and replacing with a single title: Register Runner Command.

~performance improvements

• The instructions now are lazy loaded: The instructions are only loaded once users have clicked the button, a skeleton loaders is used while the information is loaded.

Screenshots (strongly suggested)

Before	After

In action

There are new loading indicators added when new information is about to be updated (this was recorded on a throttled network, to allow more time for the loading states):

On mobile:

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
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  • I have not included a changelog entry because _____.
• 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

Related to #326102 (closed)