docs: update contribution instructions with instructions for Docker replacements

[crowecawcaw]

Reason for this change

aws-cdk supports Docker replacements such as Finch, but the CONTRIBUTING.md guidelines don't mention it.

Description of changes

Add instructions for using Docker replacements.

Describe any new or updated permissions being added

None

Description of how you validated changes

Used the instructions myself.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[paulhcsun]

@Mergifyio update

[mergify]

update

✅ Branch has been successfully updated

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Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.98%. Comparing base (74cbe27) to head (e021020).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #34038   +/-   ##
=======================================
  Coverage   83.98%   83.98%           
=======================================
  Files         120      120           
  Lines        6976     6976           
  Branches     1178     1178           
=======================================
  Hits         5859     5859           
  Misses       1005     1005           
  Partials      112      112           

Flag	Coverage Δ
suite.unit	83.98% <ø> (ø)

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Components	Coverage Δ
packages/aws-cdk	∅ <ø> (∅)
packages/aws-cdk-lib/core	83.98% <ø> (ø)

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[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: e021020
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

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