Add new mcp3221 analog sensor docs

[philippderdiedas]

Description:

This adds documentation for new mcp3221 adc sensor (see esphome pr)

Related issue (if applicable): -

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

• esphome/esphome#7764

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.

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

[netlify[bot]]

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[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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