Add support for datadog.profiling

[szegedi]

What this PR does / why we need it:

Adds support for datadog.profiling variable to enable Continuous Profiler in pods.

Allows Continuous Profiler to be enabled (or disabled) by Helm Charts config on the controller pod. The cluster-agent, running on the controller pod, will read an environment variable and use this to mutate the configuration of other pods to set the environment variables that will activate profiling within the tracer/profiler client libraries.

• This PR depends on cluster-agent interpreting the environment variable: PROF-10073: Read and propagate helm config for profiling datadog-agent#27185

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• Chart Version bumped
• Documentation has been updated with helm-docs (run: .github/helm-docs.sh)
• CHANGELOG.md has been updated
• Variables are documented in the README.md
• For Datadog Operator chart or value changes update the test baselines (run: make update-test-baselines)

[eliottness]

After the reading the doc you created. I don't think this if does what you want it to do about nil values. cf helm chart docs

[szegedi]

I think it does what I want (omits the env var on null), but it doesn't do what I want for "false" (which would be emitting explicit "false" value, but it also omits the env var) so I need to change that. Right now it's:

% helm template ./datadog --set datadog.profiling.enabled=null | grep PROFILING -A 1
% helm template ./datadog --set datadog.profiling.enabled=false | grep PROFILING -A 1
% helm template ./datadog --set datadog.profiling.enabled=auto | grep PROFILING -A 1
          - name: DD_ADMISSION_CONTROLLER_AUTO_INSTRUMENTATION_PROFILING_ENABLED
            value: "auto"
% helm template ./datadog --set datadog.profiling.enabled=true | grep PROFILING -A 1
          - name: DD_ADMISSION_CONTROLLER_AUTO_INSTRUMENTATION_PROFILING_ENABLED
            value: "true"

but with a change to the predicate to say {{- if not (eq .Values.datadog.profiling.enabled nil) }} it's doing what I'd expect it to. If there's maybe some other aspect that I'm not seeing, please let me know.

[eliottness]

If you follow the implementation ASM did in the cluster-agent then it will only trigger on pod with SSI and not those with manually installed library. Injecting vars into manually installed pods should be done by the end of Q3 following the work done by APM on service discovery.

[szegedi]

I pretty much took over the comment from the ASM part as well – it, too, says "either manually or via Single Step Instrumentation" so I guess it should say the same in both places?