CI template for installing cluster applications

What does this MR do?

Adds a new CI template to install cluster applications.

• This has the advantage of surfacing install logs to the user
• Also, this has the feature of allowing users to customize the installation via helm values

Related issue: #7983 (closed)

Uses docker image from https://gitlab.com/gitlab-org/cluster-integration/cluster-applications (MIT licensed)

Screenshots

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