Support for Event entity messages

[nohat]

Add support for Event entities:

• message ListEntitiesEventResponse
• message EventResponse

Related issues:

• This is part of implementation of esphome/feature-requests#2433
• Implementation in ESPHome core esphome/esphome#6451
• ESPHome documentation: esphome/esphome-docs#3722

TK: PR for changes to home-assistant core which use these messages

[jesserockz]

@nohat can you put up a draft ha core pr so we have something to reference and test with?

[esphome[bot]]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks :+1:

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