Add debug dependency to gemfiles

[p-datadog]

What does this PR do?

Adds dependency on debug

Motivation:

I would like to use a debugger in dd-trace-rb

Change log entry
None

Additional Notes:

This replaces the earlier byebug addition request (#4188)

How to test the change?
N/A

[datadog-datadog-prod-us1]

Datadog Report

Branch report: debug-dep
Commit report: ce50a1c
Test service: dd-trace-rb

✅ 0 Failed, 22431 Passed, 1488 Skipped, 5m 26.17s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-16 21:07:22

Comparing candidate commit ce50a1c in PR branch debug-dep with baseline commit 3d54001 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 31 metrics, 2 unstable metrics.

[TonyCTHsu]

If you do not need this gem to be added to all the gemfiles, have you consider placing it within the dev group from the gemfiles at root?

[p-datadog]

Some of the integrations had a dependency on byebug which serves the same function - I replaced it with a dependency on debug to be consistent.

[p-datadog]

I also removed byebug requires because they existed in a minority of applications. If we want the debugger to be always required I can do that everywhere.