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