Deprecate implicit state_topic for MQTT discovery

[emontnemery]

Breaking Change:

MQTT discovery will not longer implicitly set state_topic except for mqtt.alarm_control_panel, mqtt.binary_sensor and mqtt.sensor.

Description:

MQTT discovery implicitly sets state_topic, this is not documented, not covered by any tests and breaks implicit optimistic mode.

This PR:

• Does not implicitly set state_topic for components where a state_topic is not required, i.e. where implicit optimistic mode is possible.
• Prints a warning message when a state_topic is implicitly set
• Adds tests

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.

If the code does not interact with devices:

• Tests have been added to verify that the new code works.

[github-actions]

Hey there @home-assistant/core, mind taking a look at this pull request as its been labeled with a integration (mqtt) you are listed as a codeowner for? Thanks!

[codecov]

Codecov Report

Merging #22998 into dev will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev   #22998      +/-   ##
==========================================
+ Coverage   93.95%   93.98%   +0.03%     
==========================================
  Files         448      449       +1     
  Lines       36750    36763      +13     
==========================================
+ Hits        34529    34553      +24     
+ Misses       2221     2210      -11

Impacted Files	Coverage Δ
homeassistant/components/mqtt/climate.py	99.49% <ø> (-0.01%)	⬇️
homeassistant/components/mqtt/camera.py	100% <ø> (ø)	⬆️
homeassistant/components/mqtt/discovery.py	97.93% <100%> (+0.04%)	⬆️
homeassistant/components/mqtt/lock.py	91.83% <0%> (-8.17%)	⬇️
homeassistant/loader.py	94.11% <0%> (-0.2%)	⬇️
homeassistant/helpers/service.py	93.19% <0%> (-0.08%)	⬇️
homeassistant/components/google_assistant/trait.py	96.1% <0%> (-0.05%)	⬇️
homeassistant/helpers/entity_component.py	96.18% <0%> (-0.03%)	⬇️
homeassistant/components/deconz/deconz_device.py	100% <0%> (ø)	⬆️
homeassistant/helpers/aiohttp_client.py	95.34% <0%> (ø)	⬆️
... and 9 more

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