This commit adds a feature flag, `ci_job_trace_force_encode`, that will
ensure that CI job traces that contain UTF-8 can be appended with
ASCII-8BIT data.

Previously we saw encoding errors when persisted job logs that contained
UTF-8 characters were appended to ASCII-8BIT data from the HTTP
request. This would cause a 500 error, but the runner would retry
indefinitely with identical PATCH requests. This commit should make the
append work and allow the job to finish.

This is the sequence of events that causes the append to be called:

1. Runner sends a `PUT /api/v4/jobs/:id` to indicate the job is canceled
or finished.

2. `UpdateBuildStateService#accept_build_state!` persists all live job
logs to object storage.

3. `UpdateBuildStateService#accept_build_state!` returns a 202 to the
runner.

4. The runner will continue to send PATCH requests with job logs until
all logs have been sent and received.

5. If the last PATCH request arrives after the job log has been
persisted, we retrieve the data from object storage to append the
remaining lines.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/333424

Changelog: fixed