Update pipeline to clear out old unused files

[DavidMcClatchey]

Description

As part of our deployment process, we do not delete previously uploaded files that have been deleted in the code base. For example, the file in Azure on the container's data storage that served https://simplereport.gov/getting-started/staying-connected/ did not get deleted when the corresponding file was removed in the git code base.

Expected behavior

The new behavior should be that any files that are no longer in use get deleted as part of the deployment process.

Additional context

There may be a gotcha to this that we'd like to avoid where there's a small risk of the site appearing blank for a few seconds. See the linked Slack thread for broader context on how this issue came up.