Update Rails on Rack guide [ci skip]

Added first draft of Rails 5.2 release notes [ci skip]

This will keep the behavior of an application with the defaults of a 4.2
or 5.0 application behaving the same when upgrading to 5.2.

Since `ContentSecurityPolicy::Middleware` is not loaded in API-only
Applications, initializer is unnecessary.
Ref: https://github.com/rails/rails/blob/9c10fec4c06da38f8975dfb851f4d899aa85f8b7/railties/lib/rails/application/default_middleware_stack.rb#L66..L68

Added missing test for presence of CSP initializer

Fix CHANGELOG for CSP PR #31162 [ci skip]

- Followup of #31162

Add DSL for configuring Content-Security-Policy header

The def with blank `()` was newly added in #31176, but we have not used
the blank `()` style in most part of our code base.
So I've enabled `Style/DefWithParentheses` to prevent to newly added the
code.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy

Use Puma 3.11 in newly generated applications

In order to use early hints, need to use Puma 3.11.0 or higher.
So, I think that should specify that version in newly generated applications.

Ref: https://github.com/puma/puma/commit/f6f3892f4d82638fb7a2a57d993641b1486ee88a

Clean database naming ambiguity

Add new error class `QueryCanceled` which will be raised when canceling statement due to user request (#31235)

This changes `StatementTimeout` to `QueryCanceled` for PostgreSQL.

In MySQL, errno 1317 (`ER_QUERY_INTERRUPTED`) is only used when the
query is manually cancelled.

But in PostgreSQL, `QUERY_CANCELED` error code (57014) which is used
`StatementTimeout` is also used when the both case. And, we can not tell
which reason happened.

So I decided to introduce new error class `QueryCanceled` closer to the
error code name.

Since #31129, new error class `StatementTimeout` has been added.
`TransactionTimeout` is caused by the timeout shorter than
`StatementTimeout`, but its name is too generic. I think that it should
be a name that understands the difference with `StatementTimeout`.

Remove field ids from scaffold form

This reverts commit 0f79ab91, reversing
changes made to d575f7f2.

This PR philosophically conflicts with #30800 and Matthew thinks we
should hold off merging this until we find concensus. Reverting since
we're about to cut a release for 5.2.

In some places this file referred to the database in three different ways: database, DB and db. The last one caused confusion with the db namespace and the db folder. This commit removes this ambiguity by using the whole word 'database' everywhere

This reverts commit 536d3068.

Flush idle database connections

minor Engines guide copyedits: neutral language,  verb tense, comma splice [ci skip]

This was added with 27f103fc for link labels and fields.
However, `form_with` changed to generates ids by default with d3893ec3.
So I think that adding an explicit ids is unnecessary.

When load `5.1` config, `form_with_generates_remote_forms` is set.
https://github.com/rails/rails/blob/89a209f1abba5a2320d31c4898dea150c0abd0c0/railties/lib/rails/application/configuration.rb#L86

Provide arguments to RecordNotFound

Fix names of http authentication modules in api only guides

form_with_generates_ids