Make bin/dev available (but not necessary) to run solid_queue

[nimmolo]

This makes the Rails 7 standard script ./bin/dev available, and adds a Procfile.dev with one task that will start solid_queue in dev.

Note

Unlike the Rails 7 default behavior, this MO bin/dev does not start the dev server, because running the server via foreman makes debug unusable. So if someone wanted to start solid_queue locally, they could call rails s in one window, and bin/dev in another.

Admittedly, typing bundle exec rake solid_queue:start is not that much harder than typing ./bin/dev. But the Procfile can potentially have a list of tasks that run when the dev server starts. In the future this is likely what we will want to use to build the SCSS, start redis, action_cable, etc.

The idea of the PR is to make bin/dev an option, and simplify my current branch switching, where these files keep disappearing.

[coveralls]

coverage: 94.446%. remained the same
when pulling 7695437 on nimmo-bin-dev
into 40c4cd3 on main.