do not use ratelimiter for bots (#3439)

* do not use ratelimiter for bots

i tried some other approaches as having optional ratelimiter
or handle `can_send()` for bots differently,
but all that results in _far_ more code and/or indirections -
esp. as the "bot" config can change and is also persisted -
and the ratelimiter is created
at a point where the database is not yet available ...

of course, all that could be refactored as well,
but this two-liner also does the job :)

* update CHANGELOG

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Changes
 - limit the rate of MDN sending #3402
+- ignore ratelimits for bots #3439
 - remove `msgs_mdns` references to deleted messages during housekeeping #3387
 
 ### Fixes