Document trigger templating

[emontnemery]

Proposed change

Document trigger templating:

• Limited templates (Support templating MQTT triggers core#45614)
• trigger_variables (Support templating MQTT triggers core#45614)
• variables passed to wait_for_trigger (Support templating MQTT triggers core#45614)
• Templating of event triggers (Support templates in event triggers core#46207)
• Templating of MQTT triggers (Support templating MQTT triggers core#45614)

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logo's and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

• Link to parent pull request in the codebase:
• Link to parent pull request in the Brands repository:
• This PR fixes or closes issue:

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.