EMQX-9152 optimize mria running nodes

[SergeTupchiy]

No description provided.

[SergeTupchiy]

In general, this should give slightly stronger guarantee, that Node is ready to receive a ping.
Previously it was calling mria_sup:is_running/0 which checks if mria_sup is a registered process.
However, supervisor process is registered at the early stage: before its init returns and all the children are started (https://github.com/emqx/otp/blob/emqx-OTP-25.1.2/lib/stdlib/src/gen.erl#L192).
Thus, it was possible to send a cast message to mria_membership server on another node when mria_sup was already running but mria_membership was not yet.

[ieQu1]

Nit (coding style):

Suggested change

	, ?snk_meta := #{node := ObserveNode}}
	),
	, ?snk_meta := #{node := ObserveNode}
	}),

[SergeTupchiy]

Thanks, fixed.

[ieQu1]

Can it be done via mria_config:callback() ?

[SergeTupchiy]

Yes, but I think it will rather differ from existing callbacks both semantically and name-vise:

-type callback() :: start
                  | stop
                  | {start | stop, mria_rlog:shard()}
                  | core_node_discovery.

Adding something like is_mria_membership_running will not explain on which event this callback is expected to be called.
Also, all callbacks are now only used outside Mria (no callback is registered within Mria), but this one would seem to be private (I think we don't want to allow changing the way Mria is going to check if mria_membership is already running on anther node).

My intention of adding it to mria_node module was to (hopefully) raise some awareness that mria_node:is_running/0 may be not perfect in all the cases, so a developer is encouraged to implement a specific boolean function and use it with mria_node:is_running/3 ...

[ieQu1]

Suggested change

	-spec is_running(node(), atom(), atom()) -> boolean().
	-spec is_running(node(), module(), atom()) -> boolean().

[SergeTupchiy]

Fixed

[ieQu1]

Suggested change

	}).
	}).

[SergeTupchiy]

Fixed