Developer Guide restructure

[trexfeathers]

📚 Documentation

Worked out during my work on Diataxis - #6511 - but would have been scope-creep if included there.

Section rename to Get Involved

• developers_guide/contributing_code_formatting.rst -> get_involved/code/code_formatting.rst
• developers_guide/contributing_deprecations.rst -> get_involved/code/deprecations.rst
• developers_guide/documenting/docstrings.rst -> get_involved/code/docstrings.rst
• community/index.rst -> get_involved/community.rst
• developers_guide/contributing_documentation_easy.rst -> get_involved/docs/documentation_easy.rst
• developers_guide/contributing_documentation_full.rst -> get_involved/docs/documentation_full.rst
• developers_guide/contributing_documentation.rst -> get_involved/docs/index.rst
• developers_guide/documenting/rest_guide.rst -> get_involved/docs/rest_guide.rst
• developers_guide/github_app.rst -> get_involved/github_app.rst
• developers_guide/gitwash/configure_git.rst -> get_involved/gitwash/configure_git.rst
• developers_guide/gitwash/development_workflow.rst -> get_involved/gitwash/development_workflow.rst
• developers_guide/gitwash/forking.rst -> get_involved/gitwash/forking.rst
• developers_guide/gitwash/git_intro.rst -> get_involved/gitwash/git_intro.rst
• developers_guide/gitwash/index.rst -> get_involved/gitwash/index.rst
• developers_guide/gitwash/set_up_fork.rst -> get_involved/gitwash/set_up_fork.rst
• developers_guide/contributing_getting_involved.rst -> get_involved/index.rst
• developers_guide/release.rst -> get_involved/release.rst
• developers_guide/release_do_nothing.rst -> get_involved/release_do_nothing.rst
• developers_guide/contributing_pull_request_checklist.rst -> get_involved/submit/pull_request_checklist.rst
• developers_guide/documenting/whats_new_contributions.rst -> get_involved/submit/whats_new_contributions.rst
• developers_guide/contributing_benchmarks.rst -> get_involved/tests/benchmarks.rst
• developers_guide/contributing_ci_tests.rst -> get_involved/tests/ci.rst
• developers_guide/contributing_graphics_tests.rst -> get_involved/tests/graphics_tests.rst
• developers_guide/contributing_pytest_conversions.rst -> get_involved/tests/pytest_conversions.rst
• developers_guide/contributing_running_tests.rst -> get_involved/tests/running_tests.rst
• developers_guide/contributing_tests.rst -> get_involved/tests/writing_tests.rst
• further_topics/ux_guide.rst -> get_involved/ux_guide.rst
• voted_issues.rst -> get_involved/voted_issues.rst