feat: add MQTT keepalive_interval config to allow custom value per bridge #7283

Job	Run time
Block fixup commits	7s
Filter changes	3s
Check whether Cargo.lock is up to date	23s
Spell Check with Typos	4s
Shellcheck	6s
Run cargo test	11m 46s
Run cargo audit	9s
Run cargo clippy	1m 51s
Run cargo check on MSRV	1m 41s
Sort dependencies	2m 12s
nightly / doc	1m 30s
Run format checks	5m 34s
Check markdown	0s
Check for unused dependencies	7m 17s
	32m 43s

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