chore(dbm): add injection mode environment variable

[mabdinur]

Description

Adds DD_TRACE_SQL_COMMENT_INJECTION_MODE environment variable

Checklist

• Title must conform to conventional commit.
• Add additional sections for feat and fix pull requests.
• Ensure tests are passing for affected code.
• Library documentation and/or Datadog's documentation site is updated. Link to doc PR in description.

Motivation

Design

Testing strategy

Relevant issue(s)

Testing strategy

Reviewer Checklist

• Title is accurate.
• Description motivates each change.
• No unnecessary changes were introduced in this PR.
• PR cannot be broken up into smaller PRs.
• Avoid breaking API changes unless absolutely necessary.
• Tests provided or description of manual testing performed is included in the code or PR.
• Release note has been added for fixes and features, or else changelog/no-changelog label added.
• All relevant GitHub issues are correctly linked.
• Backports are identified and tagged with Mergifyio.
• Add to milestone.

[codecov-commenter]

Codecov Report

Merging #4306 (50ee9a8) into 1.x (dd1b0cf) will decrease coverage by 0.09%.
The diff coverage is 0.00%.

❗ Current head 50ee9a8 differs from pull request most recent head 6d98328. Consider uploading reports for the commit 6d98328 to get more accurate results

@@            Coverage Diff             @@
##              1.x    #4306      +/-   ##
==========================================
- Coverage   78.24%   78.15%   -0.10%     
==========================================
  Files         745      749       +4     
  Lines       59359    59429      +70     
==========================================
+ Hits        46446    46447       +1     
- Misses      12913    12982      +69     

Impacted Files	Coverage Δ
ddtrace/profiling/profiler.py	0.00% <0.00%> (ø)
ddtrace/settings/database_monitoring.py	0.00% <0.00%> (ø)
tests/internal/test_database_monitoring.py	0.00% <0.00%> (ø)
tests/profiling/gunicorn-app.py	0.00% <0.00%> (ø)
tests/profiling/test_gunicorn.py	0.00% <0.00%> (ø)
ddtrace/internal/telemetry/writer.py	76.71% <0.00%> (+0.68%)	⬆️

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