Add installer (based on Igniter)

[zachdaniel]

with this change, the installation instructions can be as simple as

mix igniter.install sentry --dsn "your_dsn"

For the release task change, a notice is emitted instructing the user to add the relevant task to their release process.

All good if you'd rather not add this change, but the installation steps for sentry were a great candidate for an installer.

My next steps would be:

1. either to contribute this package the necessary telemetry listeners to trace Ash applications automatically
2. create an ash_sentry package that composes this installer and adds the necessary integration.

We can talk about Ash integration in a separate issue, just thought that I'd explain where I'm looking to go.

[zachdaniel]

Oh, and you can test it yourself creating a new app:

mix igniter.new my_app --with phx.new --install sentry@github:zachdaniel/sentry-elixir

[zachdaniel]

I forgot to explain the main endgame which is to put sentry as an option on the https://ash-hq.org installer

[whatyouhide]

I like the direction!

[zachdaniel]

Also realized I was missing some pieces here to make the installer idempotent, will have some new code to look at shortly.

[zachdaniel]

Something also to keep in mind is that for users who don't want to use igniter or can't for whatever reason, this shouldn't affect them at all given that it is an optional dependency. What we typically do is add a tabset to our installation guides, one for "with igniter (recommended)" and one for "manual". https://hexdocs.pm/ash/get-started.html#create-a-new-project

[whatyouhide]

Nope, this looks good now. @sl0thentr0py you Sentry folks ok with this? Should help conversion ahah! 😄