This release provides the configurable option to support multitenancy.

To enable support, inside `git-pr.toml`:

```
create_repo = "user"
```

BREAKING CHANGE

We have moved repos from `git-pr.toml` to our database.  Repos will be
created on-the-fly when admins create patch requests.  We also provide
an SSH command `ssh pr.pico.sh repo create [name]` to create the repo
before a PR has landed.

chore: remove dead code

refactor: patch requests -> patchsets -> patches

Previously a patch request contained a series of patches.  This worked
great as an MVP but we are starting to see some issues with this impl.

Previously the contrib and reviewer would push patches to git-pr similar
to github pull requests.  They all get merged into a single patchset.
This mostly works until you want to start editing previous commits to
keep the commit history tidy and relevant.  For many workflows, going
back to a previous commit and amending it to address feedback is
desirable.

This creates a new model, patchset, which is a mostly immutable
container for patches.  1-to-many patch request to patchsets and
1-to-many patchset to patches.  Think of these patchsets as revisions.

This allows us to better organize collaboration and enable features like
`git range-diff` to see changes between revisions.

BREAKING CHANGE: sqlite dbs will have to be recreated as the new models
are fundamentally different. Sorry for the inconvenience!