_rollback.haml

This API can be used for manually creating deployments, instead of being
limited to creating deployments using CI pipelines.

As part of these changes, I refactored some parts of the existing
deployments code. This ensures we reuse the same logic for creating
deployments in different places. We also move the deployments service
classes to a Deployments namespace, now that there are two service
classes.

We also make some changes to which deployments are displayed. Prior to
these changes, only deployments that were successful were displayed.
This can get very confusing when using deployments from external
systems, so we now show deployments regardless of their status. The
table to display deployments has also had some style/content changes to
display the deployments data in a more meaningful way.