Add cluster agent show page

What does this MR do?

Related to issue: #321702 (closed)

We are adding a new Agent#show page. See related design

This MR will:

• Add route and controller for new page
• Add new web_path field to cluster agent GraphQL. This will be used in a follow-up MR
• Updated navbar to include new route
• Add view page, js entrypoint, vue, and graphql files to display cluster agent and associated token table
• Update associated tests and translations

Review app

(may go down)

• Agent 1: https://gitlab-review-298748-age-i5tkgg.gitlab-review.app/root/agent-show-test/-/cluster_agents/agent-no-token
• Agent 2: https://gitlab-review-298748-age-i5tkgg.gitlab-review.app/root/agent-show-test/-/cluster_agents/agent-with-tokens

Screenshots (strongly suggested)

clusterAgent

webPath

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

Related to #298748 (closed)