APM: do not replace tags on special dd tags

[ajgajg1134]

What does this PR do?

Alters the behavior of "match all" rules for replace_tags config such that they no longer affect internal datadog tags. (ie. those that start with "_."). Note that it is still possible to use replace tags on specific hidden tags if that's required (this should not ever be required, but is left as an option "just in case"), just target the specific tag directly with a replace tags rule.

Motivation

We rely on hidden tags for various product features within APM, some customers with very strict replace tags rules experienced broken APM features when these rules unexpectedly replaced important datadog tags.

Additional Notes

Possible Drawbacks / Trade-offs

It's possible someone is relying on the ability to redact data even within internal datadog tags, but this really should NOT be the case, and if they absolutely must do so then they are able to redact specific tags explicitly still. (But if you're reading this because you want to replace all _dd. tags please let us know via support so we can help support your exact use case!)

Describe how to test/QA your changes

New unit tests change covers this change well!

[pr-commenter]

Test changes on VM

Use this command from test-infra-definitions to manually test this PR changes on a VM:

inv create-vm --pipeline-id=34167294 --os-family=ubuntu

[pr-commenter]

Regression Detector

Regression Detector Results

Run ID: cd630e84-2bb3-4547-89a5-ff9d1bd17a6e
Baseline: 854f002
Comparison: 7c7d2ff

Performance changes are noted in the perf column of each table:

• ✅ = significantly better comparison variant performance
• ❌ = significantly worse comparison variant performance
• ➖ = no significant change in performance

No significant changes in experiment optimization goals

Confidence level: 90.00%
Effect size tolerance: |Δ mean %| ≥ 5.00%

There were no significant changes in experiment optimization goals at this confidence level and effect size tolerance.

Experiments ignored for regressions

Regressions in experiments with settings containing erratic: true are ignored.

perf	experiment	goal	Δ mean %	Δ mean % CI
➖	file_to_blackhole	% cpu utilization	-0.62	[-1.76, +0.52]

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI
➖	tcp_syslog_to_blackhole	ingress throughput	+15.94	[-6.98, +38.86]
➖	pycheck_1000_100byte_tags	% cpu utilization	+2.94	[-1.83, +7.71]
➖	basic_py_check	% cpu utilization	+0.11	[-2.28, +2.49]
➖	uds_dogstatsd_to_api	ingress throughput	+0.02	[-0.19, +0.22]
➖	trace_agent_json	ingress throughput	+0.00	[-0.01, +0.01]
➖	trace_agent_msgpack	ingress throughput	-0.00	[-0.00, +0.00]
➖	tcp_dd_logs_filter_exclude	ingress throughput	-0.03	[-0.07, +0.01]
➖	otel_to_otel_logs	ingress throughput	-0.03	[-0.40, +0.34]
➖	uds_dogstatsd_to_api_cpu	% cpu utilization	-0.23	[-3.03, +2.57]
➖	file_tree	memory utilization	-0.35	[-0.44, -0.26]
➖	idle	memory utilization	-0.60	[-0.64, -0.57]
➖	file_to_blackhole	% cpu utilization	-0.62	[-1.76, +0.52]

Explanation

A regression test is an A/B test of target performance in a repeatable rig, where "performance" is measured as "comparison variant minus baseline variant" for an optimization goal (e.g., ingress throughput). Due to intrinsic variability in measuring that goal, we can only estimate its mean value for each experiment; we report uncertainty in that value as a 90.00% confidence interval denoted "Δ mean % CI".

For each experiment, we decide whether a change in performance is a "regression" -- a change worth investigating further -- if all of the following criteria are true:

1. Its estimated |Δ mean %| ≥ 5.00%, indicating the change is big enough to merit a closer look.

2. Its 90.00% confidence interval "Δ mean % CI" does not contain zero, indicating that if our statistical model is accurate, there is at least a 90.00% chance there is a difference in performance between baseline and comparison variants.

3. Its configuration does not mark it "erratic".

[aliciascott]

@ajgajg1134 Just a quick suggestion for spelling, please request re-review when updated, thanks!

[aliciascott]

looks good

[knusbaum]

LGTM

[ajgajg1134]

/merge

[dd-devflow]

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