* frame/authority-discovery: Have authorities() return both current and next

Authority address lookups on the DHT happen periodically (every 10
mintues) and are rather slow (~10 seconds).

In order to smooth the transition period between two sessions, have the
runtime module return both the current as well as the next authority
set. Thereby the client authority module will:

1. Publish its addresses one session in advance.

2. Prefetch the addresses of authorities of the next session in advance.

* frame/authority-discovery: Deduplicate authority ids

* frame/authority-discovery: Don't dedup on_genesis authorities

* frame/authority-discovery: Remove mut and sort on comparison in tests

* frame/authority-discovery: Use BTreeSet for deduplication

With authority-discovery moving from a poll based future to an `async`
future Rust has difficulties propagating the `Sync` trade through the
generated state machine.

Instead of using dynamic dispatching, use a trait parameter to specify
the DHT event stream.

* Ensure that handshake is sent back even in case of back-pressure

* Update client/network/src/protocol/generic_proto/handler/group.rs

Co-authored-by: Max Inden <[email protected]>

* Also process OpenRequest and Closed

* Fix bad merge

* God I'm so lost with all these merges

* Immediately return Closed

Co-authored-by: Max Inden <[email protected]>

Also renamed KeystoreParams to KeystoreContainer

* *: Update to Prometheus v0.10.0-rc.1

* *: Update to Prometheus v0.10.0

* ci: deploy alerting rules: fix run on changes

Co-authored-by: Max Inden <[email protected]>

* Silence the error about non-registered protocols

* Silence the other two locations as well

Fixing #6988

* update bip39 version

* and lock

* client/cli/src/config: Warn on low file descriptor limit

Substrate sets the soft file descriptor limit to the hard limit at
startup. In the case of the latter being low already (< 10_000) a
Substrate node under high demand might run into issues e.g. when opening
up new TCP connections or persisting data to the database.

With this commit a warn message is printed to stderr.

* client/cli/Cargo.toml: Update to fdlimit 0.2.0

* client/*: Treat protocol name as str and not [u8]

Notification protocol names are in practice always valid utf8 strings.
Instead of treating them as such in the type system, thus far they were
casted to a [u8] at creation time.

With this commit protocol names are instead treated as valid utf8
strings throughout the codebase and passed as `Cow<'static, str>`
instead of `Cow<'static, [u8]>`. Among other things this eliminates the
need for string casting when logging.

* client/network: Don't allocate when protocol name is borrowed