updated documentation for Geo

This is part of the refactor to include a RollbackService into
HashedStorage module

We still rely on the Dirty API for project rename (before/after) values,
but we don't access the dirty api from the service class anymore.

The previous value is now part of the initialization, which makes it
easier to test and the behavior is clearer.

The same was done with the `rename_repo` on the Storage classes, we now
provide before and after values as part of the method signature.

During a previous refactor on project model, code related to the
hashed storage was extracted into AfterRenameService, see
4b9c17f1.

The "path_before" was changed from using `previous_changes['path']` to
`path_was`. They are not equivalent. `path_was` exists reliably only
*before* persisting to the database. After database persistence is
confirmed, the value is moved to `previous_changes[:attribute_name]`.

Because the repository/attachments rename or storage upgrade happens
after it was persisted to the database, we were in fact not informing
the right parameters (and therefore not doing what it was supposed to).

This moves the logic of Project#rename_repo and all methods _only_ used
by this method into a new service class: Projects::AfterRenameService.
By moving this code into a separate service class we can more easily
refactor it, and we also get rid of some RuboCop "disable" statements
automatically.

During the refactoring of this code, I removed most of the explicit
logging using Gitlab::AppLogger. The data that was logged would not be
useful when debugging renaming issues, as it does not add any value on
top of data provided by users.

I also removed a variety of comments that either mentioned something the
code does in literal form, or contained various grammatical errors.
Instead we now resort to more clearly named methods, removing the need
for code comments.

This method was chosen based on analysis in
https://gitlab.com/gitlab-org/release/framework/issues/28. In this issue
we determined this method has seen a total of 293 lines being changed in
it. We also noticed that RuboCop determined the ABC size
(https://www.softwarerenovation.com/ABCMetric.pdf) was too great.