web_server: Update documentation for changes in PR #6269

[DanielBaulig]

Also fixed a small formatting bug in the color_temp documentation

Description:

Adds documentation for the added Cover position property, clarifies that value will only be 1.0 or 0.0 when the cover doesn't support the position trait and fix a small formatting bug in another part of the document.

Related issue (if applicable): N/A

Pull request in esphome with YAML changes (if applicable): esphome/esphome#6269

Checklist:

• [x] I am merging into next because this is new documentation that has a matching pull-request in esphome as linked above.
  or

• [ ] I am merging into current because this is a fix, change and/or adjustment in the current documentation and is not for a new component or feature.

• [ ] Link added in /index.rst when creating new documents for new components or cookbook. N/A

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[DanielBaulig]

@jesserockz This is a documentation change for the PR https://github.com/esphome/esphome/pull/6269 you accepted and merged. Mind signing off on this, too? Thanks!

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