…ed via env var (#10233)
### Change Overview
This PR enables the `wait_for_receiver` field to be set via
`DD_CRASHTRACKING_WAIT_FOR_RECEIVER` environment variable. If unset, the
default is `true`.
### Motivation
[System-tests for
crashtracking](DataDog/system-tests#2884)
exposed that the Python crashtracker needs the `wait_for_receiver` field
to be set to `true` to capture crashes and reliably send telemetry
events to the agent. While set to `false`, telemetry events for crashes
would work very rarely. When set to `true`, this would become reliably
consistent.
The value for `wait_for_receiver` is [unset in
`libdatadog`](https://github.com/DataDog/libdatadog/blob/16528ffee456f7af5fe9ad80a6294fb5dcd38918/crashtracker/src/shared/configuration.rs#L28),
which means it is set to `false` by default. This default needs to be
updated on the `libdatadog` end. However, in order to unblock
crashtracking functionality for `dd-trace-py`, we are also enabling this
to be configured on the `dd-trace-py` side as well.
## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))
## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)
(cherry picked from commit bb82a8e)