Add WS handler to generate encryption key for cloud backup

[ludeeus]

Proposed change

Adds a WS handler to create and store a string that can be used for encrypting cloud backups.

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• Dependency upgrade
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• This PR fixes or closes issue: fixes #
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[home-assistant]

Hey there @home-assistant/cloud, mind taking a look at this pull request as it has been labeled with an integration (cloud) you are listed as a code owner for? Thanks!

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[MartinHjelmare]

I'm assuming this needs a frontend change. If not, we can merge.

[MartinHjelmare]

We should rebase this to allthebackupchanges branch.

[MartinHjelmare]

Since we're using a feature branch we don't need to wait for frontend.

[emontnemery]

There's some ongoing discussion about how the cloud encryption should work, we should not merge this PR until that's been settled.

[edenhaus]

Closing it as we internally discussed that the password encryption is enough. No need for an additional cloud key