Add documentation for new integration Hanna

[bestycame]

Proposed change

Added documentation for a new integration I'm adding to Home Assistant (domain=hanna).
The Integration will connect to Hanna Cloud from Hanna Instruments in order to integrate the Pool Controller.

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 logos 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: PR #147085
• Link to parent pull request in the Brands repository: PR #7244
• This PR fixes or closes issue: Not applicable

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.

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