feat(MQTT): Add enable, disable and enable_on_boot

[Rapsssito]

What does this implement/fix?

Adds mqtt.enable and mqtt.disable actions and enable_on_boot optional parameter, just like BLE and WiFi. This PR comes after the discord discussion about #7327, allowing users to delay the MQTT component setup so they can use lambdas to adapt the configuration to their own setup.

Provides a workaround for this forum post.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code quality improvements to existing code or addition of tests
• Other

Pull request in esphome-docs with documentation (if applicable):

• feat(MQTT): Add enable, disable and enable_on_boot esphome-docs#4408

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040
• BK72xx
• RTL87xx

Example entry for config.yaml:

# Example config.yaml
esphome:
  on_boot:
    - priority: -100
      then:
        - mqtt.enable
        - delay: 20s
        - mqtt.disable
        - delay: 20s
        - mqtt.enable
       
mqtt:
  broker: "192.168.178.84"
  port: 1883
  username: debug
  password: debug
  enable_on_boot: false

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.98%. Comparing base (4d8b5ed) to head (26c6d9c).
Report is 1555 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #7716      +/-   ##
==========================================
+ Coverage   53.70%   53.98%   +0.27%     
==========================================
  Files          50       50              
  Lines        9408     9766     +358     
  Branches     1654     1344     -310     
==========================================
+ Hits         5053     5272     +219     
- Misses       4056     4170     +114     
- Partials      299      324      +25     

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