Add git to prepare performance testing

[maxday]

What does this PR do?

Add git to Dockerfile to allow installing specific dd-trace version (by git hash)

Motivation

Prepare for performance testing

Testing Guidelines

CI should pass

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)

[codecov-commenter]

Codecov Report

Merging #332 (f2676e4) into main (73cd8aa) will not change coverage.
The diff coverage is n/a.

❗ Current head f2676e4 differs from pull request most recent head 43ee833. Consider uploading reports for the commit 43ee833 to get more accurate results

@@           Coverage Diff           @@
##             main     #332   +/-   ##
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  Coverage   79.02%   79.02%           
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  Files          36       36           
  Lines        1807     1807           
  Branches      418      418           
=======================================
  Hits         1428     1428           
  Misses        326      326           
  Partials       53       53           

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