Fixes #23757.

Before this commit, even if `reject` was called in the `subscribe`
method for an Action Cable channel, all actions on that channel could
still be invoked. This calls a `return` if a rejected connection tries
to invoke any actions on the channel.

Style/SpaceBeforeBlockBraces
Style/SpaceInsideBlockBraces
Style/SpaceInsideHashLiteralBraces

Fix all violations in the repository.

Inserted spaces in the name of Rails components.

Since I was on it, also used PostgreSQL instead of Postgres
because albeit Postgres is an accepted alias, PostgreSQL is
the official name and the actual name of the adapter.

See

    https://wiki.postgresql.org/wiki/ProjectName

with regard to PostgreSQL vs Postgres.

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

[ci skip]

Require our dependency and forgo the core ext version.

Follow up to #25240.

- Only Action Cable README did not have this section, all of the other
  READMEs have this section.

- Remove "Configuration", "Running the server", "Dependencies" and "Deployment"
  sections from the Action Cable README as they are already duplicated in the
  Action Cable overview guide.

[Javan Makhmali, Jon Moss]

Cuts down the number of concurrent Sauce Labs VMs we need to spin up. Can add specific versions back in to target regressions if need be.

Added 'sh' for markdown formatting as bash.

Sorry, forgot to include in my main PR :(

[ci skip]

[Jon Moss, Zach Schneider]