Reorganize the packages and general housekeeping

What does this MR do?

This change does not make change any existing feature. It mainly reorganizes the current packages into a new structure.

In this structure:

1. api/v2alpha1 is broken down into multiple files across various components and features. The package name hasn't changed.
2. Packages in pkg/ are moved into internal/pkg/. The hierarchical structure of these packages is flattened for verbosity.
3. The internal/controllers package now includes workflows and functions. The former is the GitLab-specific tasks and workflows and the latter contains GitLab-specific template functions.

It also contains a two minor refactoring:

1. InstallApplicationServer and InstallJobProcessor workflows implement Task interface. This is simply done by adding a return value.
2. Application configuration tasks are pulled into a new workflow, ConfigureApplication. The reconcile loop now looks shorter and more readable.

The majority of other changes are adjusting the import section to point to the relocated packages.

Author's Checklist

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Ensure a release milestone is set.
• MR title and description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• MR has a green pipeline on GitLab.com.
• When ready for review, MR is labeled workflowready for review per the MR workflow.

Expected

• Test plan indicating conditions for success has been posted and passes.
• Documentation is created or updated.
• Tests are added.

Related issues

Closes #39 (closed)