Update Kubernetes agent registration dialog

What does this MR do and why?

Main changes

This MR updates the agent registration process. It removes the agent selector from the registration modal. Now the user needs to type the agent name to register it. We also updated the modal copy and links.

When the agent is registered we now show the success alert with some details on where to create the agent's configuration.

Additional changes to support the requirements:

• The KAS disabled error handling moved to the agents.vue component as it's now the only related request. The error is provided to the modal to maintain the UI.
• Once the agent is created from the modal, we emit an event with the agent name to render the success alert in the agents.vue component.
• The queries and mutations updated to have both CE and EE variants to support the newly added isReceptive field. This is not directly related to the current MR, but I had to make this change here as we are updating the agents list on the agent creation by modifying the Apollo cache, and it fails with the errors on missing fields.
• The agent selector dropdown and related specs and constants were removed.

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• Re-evaluate Kubernetes agent registration dialog (#506444 - closed)
• ✨ Beautifying our UI (17.7-17.8) ✨ (#506374 - closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After
Screen_Recording_2024-12-16_at_14.26.42	Screen_Recording_2024-12-16_at_14.12.56

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Enable KAS on your GDK (steps 1-2 from the guide).
2. Visit the Project -> Infrastructure -> Kubernetes clusters page and select the "Connect a cluster" button.
3. Verify the registration modal.
4. Continue with the instructions in the modal and close the modal once done.
5. Verify the success popup is shown with the agent name and details on how to create and agent config file.

Related to #506444 (closed) and #506374 (closed)