Add support for fetching bindkey from Mi cloud

[bdraco]

TODO

• [ ] bump xiaomi-ble after merging linked PR
• [ ] tests
• [ ] docs

Proposed change

needs https://github.com/Bluetooth-Devices/xiaomi-ble/pull/98

Type of change

• [ ] Dependency upgrade
• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] New integration (thank you!)
• [x] New feature (which adds functionality to an existing integration)
• [ ] Deprecation (breaking change to happen in the future)
• [ ] Breaking change (fix/feature causing existing functionality to break)
• [ ] Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

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[home-assistant[bot]]

Hey there @jc2k, @ernst79, mind taking a look at this pull request as it has been labeled with an integration (xiaomi_ble) you are listed as a code owner for? Thanks!

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[bdraco]

thanks. I'll adjust as needed in a followup if testing shows any changes are needed.