A feature flag can be marked as "auto-enable" by setting `auto_enable` to
true in its properties.

An auto-enable feature flag is automatically enabled as soon as all
nodes in the cluster support it. This is achieved by trying to enable it
when RabbitMQ starts, when a plugin is enabled/disabled or when a node
joins/re-joins a cluster. If the feature flag can't be enabled, the
error is ignored.

An auto-enable feature flag also implicitly depends on
`feature_flags_v2`.

However, it should be used cautiously, especially if the feature flag
has a migration function, because it might be enabled at an
inappropriate time w.r.t. the user's workload.

Remove a one-liner

@kjnilsson:

> why that line of code is a oneliner I have no idea
> should really be a pattern match in the function head

Refactor quorum queue periodic metric emission

Support management path prefix when using OAuth2

Update Stream protocol document

Fix docs for rabbitmqctl restart_vhost

As per conversation with @acogoluegnes, the frame `SaslHandshakeRequest` does not have a field `mechanism`. This field actually used in `SaslHandshakeResponse` and `SaslAuthenticateRequest` frames.

Primarily to avoid the transient process that is spawned every
Ra "tick" to query the quorum queue process for information that could
be passed in when the process is spawned.

Refactored to make use of the overview map instead of a custom
tuple.

Also use ets:lookup_element where applicable