Fix a regression in parsing ignore.resources for traces

[bmermet]

What does this PR do?

This PR addresses a regression in the parsing of the ini configuration for the trace agent introduced in #2698.

It used to accept strings normal strings, but now requires them to be escaped with quotes. Meaning that:

[trace.ignore]
resource: config.get_config

used to work but is now broken. And given the ini parser strips quotes, the only way I've found to parse a single resource is to do:

[trace.ignore]
resource: '"/health"'

It currently works for multiple resources with the format:

[trace.ignore]
resource: "/health","/500"

But this is not backward compatible with the previous version that was:

[trace.ignore]
resource: "/health,/500"

Motivation

This PR reverts the original behavior to avoid having a non backward compatible change.

Additional Notes

[bits-bot]

All committers have signed the CLA.

[arbll]

Nit: use back-ticks to be able to write raw strings without need for escaping

[arbll]

A few nits, apart from them, looks good to me

[arbll]

You should probably use them for every config to stay consistent and make reading easier

[arbll]

could you just return r.Read() ?

[bmermet]

Indeed, silly me. I copy pasted this from the trace-agent without giving it a thought.

[arbll]

LGTM - For anyone looking at this PR and seeing the critical label: there is no impact on the version 6 of the agent. This code is shared with the datadog-trace-agent and impacts the version 5 of the agent.

[olivielpeau]

Note: this PR has a small impact on Agent 6, since it affects the datadog-agent import command. How does the bug affect users that that have an Agent 5 ini config with resource set under [trace.ignore] and run the datadog-agent import command?

[bmermet]

The bug indeed breaks the import command for people who use it on a iniconfig affected by the bug. It will exit with this error: https://github.com/DataDog/datadog-agent/blob/master/cmd/agent/common/import.go#L67.

[arbll]

Let's add a bugfix release note to this PR then

[codecov-io]

Codecov Report

Merging #2797 into master will increase coverage by <.01%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master    #2797      +/-   ##
==========================================
+ Coverage   57.13%   57.14%   +<.01%     
==========================================
  Files         385      383       -2     
  Lines       24746    24644     -102     
==========================================
- Hits        14139    14082      -57     
+ Misses       9671     9634      -37     
+ Partials      936      928       -8

Impacted Files	Coverage Δ
pkg/config/legacy/converter.go	92.87% <81.81%> (+0.08%)	⬆️
pkg/util/containers/metrics/cgroup_metrics.go	33.17% <0%> (-11.18%)	⬇️
pkg/collector/corechecks/containers/docker.go	0.98% <0%> (-5.04%)	⬇️
pkg/logs/input/listener/tailer.go	86% <0%> (-4%)	⬇️
pkg/config/config.go	82.08% <0%> (-0.81%)	⬇️
pkg/logs/auditor/auditor.go	71.12% <0%> (-0.71%)	⬇️
pkg/autodiscovery/providers/providers.go	100% <0%> (ø)	⬆️
pkg/util/kubernetes/apiserver/controllers.go	0% <0%> (ø)	⬆️
pkg/util/containers/metrics/disk.go
pkg/autodiscovery/providers/kube_services.go
... and 4 more