Fix code owners to capture deep changes and force absolute paths

[AlexJF]

What does this PR do?
Existing code owners did not work as intended with changes exclusive to deep nested files and may match on unintended files due to lack of absolute path usage (e.g. any nested ext dir would be attributed to profiling).

Refer to the example to see why the existing rules were wrong:

# The `docs/*` pattern will match files like
# `docs/getting-started.md` but not further nested files like
# `docs/build-app/troubleshooting.md`.
docs/*  [email protected]

# In this example, @octocat owns any file in an apps directory
# anywhere in your repository.
apps/ @octocat

# In this example, @doctocat owns any file in the `/docs`
# directory in the root of your repository and any of its
# subdirectories.
/docs/ @doctocat

Motivation:
Proper tagging of relevant reviewers. Here's an example where the existing rules did not target @Datadog/profiling-rb but should have: #3352

Additional Notes:

How to test the change?

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[ivoanjo]

👍 LGTM thanks for spotting this!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5899696) 98.24% compared to head (ac1f680) 98.24%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3363   +/-   ##
=======================================
  Coverage   98.24%   98.24%           
=======================================
  Files        1254     1254           
  Lines       73198    73198           
  Branches     3430     3430           
=======================================
+ Hits        71910    71911    +1     
+ Misses       1288     1287    -1     

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