Honor maximum message size limit of MQTT server

[underhood]

Summary

New MQTT broker on cloud size has maximum message size set to less than maximum MQTT message size.
We honor this limit now.

This gives us following change in behavior:
BEFORE:

• if cloud requested data that were too big for the MQTT broker to handle we sent it anyway leading to MQTT broker disconnecting us. This led to temporary disruption of service for user until the agent reconnected.

AFTER:

• if cloud requests data that are too big for MQTT broker we detect this and report it to cloud with special error code. This way cloud can show this to particular user (who initated the request) but all the other charts (and other users) will not experience any disruption.

Test Plan

Additional Information

For users: How does this change affect me?

[stelfrag]

Setting the limit to 32768 bytes will produce.

2023-05-12 11:15:15: netdata ERROR : ACLK_QRY[6] : [mqtt_wss] E: Message too big for server: 49021
2023-05-12 11:15:15: netdata ERROR : ACLK_QRY[6] : Failed to send cancelation message for http reply

So maybe we need to add the negotiated limit in the error message -- eg 49021 (max size = 32768) or something like that.

The next message Failed to send cancelation message for http reply is probably not correct in this case.

[underhood]

So maybe we need to add the negotiated limit in the error message -- eg 49021 (max size = 32768) or something like that. I log the maximum when we establish a connection. I try to avoid repeating the same number on every log line to make logs compact

[underhood]

rebased for conflict resolution + fixed bug

[thiagoftsm]

PR is working as expecting, LGTM!

[underhood]

after 2 approving reviews I merged changes in mqtt_websockets submodule from dev to master.
Last commit only changes submodule pointer to point to master branch 0 code changes.
@thiagoftsm @stelfrag Please re-approve at your convenience