[wiki migration] Infra team pages (#148718)

This sorts the wiki pages owned by the Infra team in the docs/ directory as planned in [flutter.dev/go/migrate-flutter-wiki-spreadsheet](https://docs.google.com/spreadsheets/d/1x65189ZBdNiLRygpUYoU08pwvXD4M-Z157c6pm8deGI/edit?usp=sharing) 

It also adds the team-infra label to the bot for future PRs.

Image assets were checked in here: https://github.com/flutter/assets-for-api-docs/pull/246

Changes to the content were only updating links. The remaining wiki links will be updated after the rest of the pages are relocated, the original wiki links still work in the meantime.

Part of https://github.com/flutter/flutter/issues/145009

docs/contributing/Labeling-PRs.md

@@ -0,0 +1,23 @@
+# Labeling PRs
+
+Across the Flutter organization, the [labeler](https://github.com/actions/labeler) GitHub action is used per repo.
+
+For repos that already use it, only `.github/labeler.yml` needs to be edited. For bringing up new repos, `.github/workflows/labeler.yml` should be copied from an existing repo into the new repo.
+
+## How to add new labels
+
+```yaml
+macos:
+  # **/* recursively searches all subdirectories and files
+  - shell/platform/darwin/macos/**/*
+
+# For complex label names, it may need to be wrapped in quotes
+'a: accessibility':
+  - **/accessibility/*
+```
+
+## Verifying changes in presubmit
+
+GitHub actions do not test changes in presubmit. To verify, copy your local change into a YAML linter to verify the file is not malformed.
+
+Once landed, you can look at new workflow runs to see if the matches are being used.