[Pipelines] Separate templates section into two modules

Context

Follow up issue from https://issues.redhat.com/browse/RHDEVDOCS-5518

Problem area

During pipelines QE review, it was observed that there are now two methods of creating pipelines templates as an admin.

One of the methods is incorrectly included in the section Using a custom pipeline template for creating and deploying an application from a Git repository which should be a section that just explains to users how to create a pipeline using the template that was created by an admin.

While this is the wrong place for the admin / template information, it's likely that this information is still useful. The new module added in RHDEVDOCS-5518 just covers adding an entirely new template to the cluster, whereas the existing information tells admins how they can re-purpose and customize existing templates without having to create a new template from scratch.

Proposed solution

• Split that existing procedure into two modules; one for admin creating templates, and one for dev using templates
• Put them in the right sections (admin perspective and dev perspective sections, all under a top level section for web console in the pipelines docs) per the PR for RHDEVDOCS-5518
• Rebase RHDEVDOCS-5518 on top of these changes to add the new module

Additional information

We will need to check with the pipelines engineering and QE team whether the older solution is actually still valid, and whether there are any UX improvements that can be made to the doc, or if the process can be simplified or updated at all.