refactor(ciapp): move common logic to ci module

[jirikuncar]

Prepare the land for adding common CI Visibility features to its own place in ddtrace.internal.ci module.

This PR removes usage of Pin on PyTest config object in preparation for more integrations. Also it makes it easier to configure tracer instance used to submit CI Visibility information by having a single entry point regardless on used testing framework.

Checklist

• [x] Added to the correct milestone.
• [x] Tests provided or description of manual testing performed is included in the code or PR.
• [ ] ~Library documentation is updated.~
• [ ] ~Corp site documentation is updated (link to the PR).~

[jirikuncar]

@Kyle-Verhoog the plan is to create a single entry point for CI Visibility instrumentation as we don't want to rely on automatic instrumentation. We will add more writers for features that are coming and use new API endpoints.

[mergify[bot]]

@jirikuncar this pull request is now in conflict 😩

[mergify[bot]]

@jirikuncar this pull request is now in conflict 😩