[ci skip] Added documentation for has_many scope parameter
[ci skip] add doc for STEP in migration
Merge pull request #16575 from tomkadwill/added_has_many_scope_documentation

[ci skip] Added documentation for has_many scope parameter
Merge pull request #16593 from aditya-kapoor/add-doc-for-step

[ci skip] add doc for STEP in migration
Merge pull request #16594 from loganhasson/master

[ci skip] Fix Active Job grammar in api docs
Remove timestamp type from generator usage

It was soft removed at 03035d69e14032a589e9653e3145237b8a9a09be
Make the explicit the Active Job dependency of Action Mailer
Update configuring.md [ci skip]

Remove ActiveRecord config instructions for active_record.attribute_types_cached_by_default, which was removed in https://github.com/rails/rails/commit/66736c8e50585
Merge pull request #16597 from teeparham/master

Remove cached attributes from Configuring guide [ci skip]

This was removed in #15429
Fix SyntaxError
"warning: assigned but unused variable"
[ci skip] Fixing spelling typo in testing guide.
Merge pull request #16600 from bradly/spelling-fix-in-testing-guide

[ci skip] Fixing spelling typo in testing guide.
Enable gzip compression by default

If someone is using ActionDispatch::Static to serve assets and makes it past the `match?` then the file exists on disk and it will be served. This PR adds in logic that checks to see if the file being served is already compressed (via gzip) and on disk, if it is it will be served as long as the client can handle gzip encoding. If not, then a non gzip file will be served.

This additional logic slows down an individual asset request but should speed up the consumer experience as compressed files are served and production applications should be delivered with a CDN. This PR allows a CDN to cache a gzip file by setting the `Vary` header appropriately. In net this should speed up a production application that are using Rails as an origin for a CDN. Non-asset request speed is not affected in this PR.
Merge pull request #16466 from schneems/schneems/gzip-action-dispatch

Enable gzip compression by default
Change 'does' to 'do'
Merge pull request #16603 from jwworth/task/fix_grammar

[ci skip] 4.2 release notes grammar fix
Avoid duplicating routes for HEAD requests.

Follow up to rails#15321

Instead of duplicating the routes, we will first match the HEAD request to
HEAD routes. If no match is found, we will then map the HEAD request to
GET routes.
Improve router test.

We should assert that routes will not be recognized if the verbs do
not match.
Merge pull request #15443 from tgxworld/preload_head_routes

Map HEAD requests to GET routes instead of duplicating GET routes.