Allow specfying pattern where to include config line

[juanazam]

Is your feature request related to a problem? Please describe.

Modify Igniter.Project.Config.configure/6 to allow a pattern to be passes so the configuration can be added within a specific block of the file passed as argument.

This is particularly useful when a config needs to be added to runtime.exs but within the if config_env() == :prod do block.

Describe the solution you'd like

There are existing implementations out there

Tower implementations:
mimiquate/tower_rollbar#86
mimiquate/tower_sentry#66
mimiquate/tower_bugsnag#60

Ash postgres: https://github.com/ash-project/ash_postgres/blob/main/lib/mix/tasks/ash_postgres.install.ex#L169-L179

Describe alternatives you've considered

No response

Additional context

No response

[zachdaniel]

We do have an option for this "deeper down", called after_predicate so it may be as simple as passing that option through. If that doesn't work then we can definitely support it explicitly in configure

[zachdaniel]

Sounds good, though, PRs welcome!