add AM2120 device type

[alexbuit]

What does this implement/fix?

This update adds the am2120 temp+humidity sensor

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)
• Other

Related issue or feature (if applicable): fixes

Pull request in esphome-docs with documentation (if applicable): esphome/esphome-docs#3559

Test Environment

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

Example entry for config.yaml:

# Example config.yaml
sensor:
  - platform: dht
    pin: GPIO36
    model: AM2120
    update_interval: 30s
    temperature:
      name: "Badkamer Temperature"
      accuracy_decimals: 1
    humidity:
      name: "Badkamer Humidity"

Checklist:

• [ x] 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:

• [x ] Documentation added/updated in esphome-docs.
  Am2120 esphome-docs#3555

[probot-esphome]

Hey there @OttoWinter, mind taking a look at this pull request as it has been labeled with an integration (dht) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (045836c) 53.70% compared to head (c80c66a) 53.70%.

Additional details and impacted files

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  Misses       4048     4048           
  Partials      299      299           

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[alexbuit]

documentation is in PR:
esphome/esphome-docs#3555

[jesserockz]

documentation is in PR: esphome/esphome-docs#3555

@alexbuit
I commented asking for a rebase of that PR, but then I looked at the contents and realised it is adding a whole new platform apge for a component that doesnt exist as this PR is only adding an extra model to the existing dht platform.