Documentation of ds248x component

[alainstark]

Description:

Documentation of ds248x component

Related issue (if applicable): fixes

Pull request in esphome with YAML changes (if applicable): esphome/esphome#6616

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 /index.rst when creating new documents for new components or cookbook.

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[nagyrobi]

Please check the linter warnings and fix them (eg. no tabs allowed).