fix: make apm config a pointer

[betterengineering]

What does this PR do?

This commit makes the APM configuration a pointer so that we can properly nil check it in the handler.

Motivation

In the Datadog Agent, we want the handler for this config to look like:

func (h *SingleStepHandler) HasSection(cr *datadoghq.DatadogInstrumentation) bool {
	return cr != nil && cr.Spec.Config.APM != nil
}

We can't currently nil check it because it's not a pointer 🤦 .

Describe your test plan

I made sure the generation works as expected:

make generate manifests

Checklist

• PR has at least one valid label: bug, enhancement, refactoring, documentation, tooling, and/or dependencies
• PR has a milestone or the qa/skip-qa label
• All commits are signed (see: signing commits)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 40.76%. Comparing base (4d64420) to head (384624a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2995   +/-   ##
=======================================
  Coverage   40.76%   40.76%           
=======================================
  Files         332      332           
  Lines       28197    28197           
=======================================
  Hits        11494    11494           
  Misses      15928    15928           
  Partials      775      775           

Flag	Coverage Δ
unittests	40.76% <ø> (ø)

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