3di | Making and reviewing a PR (backport #6967)

[mergify]

Description

Create new how-to articles for Making a pull request and Reviewing a pull request under new section Contributing to code.

These draw from several existing articles, refactoring the content and removing from the original location.

There will be an action at the end of the tickets under this issue to clean up, so that we don’t end up with any duplicates or dead ends.

Related to: #6828

Did you use Generative AI?

No

Additional Information

Documentation updates from 3di Information Solutions, agreed with Geoff and Tully.

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This is an automatic backport of pull request #6967 done by Mergify.

[mergify]

Cherry-pick of a6fdb55 has failed:

On branch mergify/bp/humble/pr-6967
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit a6fdb553.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   source/Contact.rst
	new file:   source/The-ROS2-Project/Contributing/Contributing-to-code.rst
	new file:   source/The-ROS2-Project/Contributing/Contributing-to-code/Making-a-PR.rst
	new file:   source/The-ROS2-Project/Contributing/Contributing-to-code/Reviewing-a-PR.rst
	modified:   source/The-ROS2-Project/Contributing/Developer-Guide.rst

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   source/How-To-Guides/Core-maintainer-guide.rst
	both modified:   source/The-ROS2-Project/Contributing.rst

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally