feat: add npm deploy and move backend source to /api folder

[robertsLando]

Fixes #3418

[github-actions]

Pull Request Test Coverage Report for Build 6865821291

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 21.569%

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Totals
Change from base Build 6865813205:	0.0%
Covered Lines:	3728
Relevant Lines:	18400

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💛 - Coveralls

[robertsLando]

TODOs:

• Docs
• Add npm publish to release workflow (requires token, see https://github.com/mqttjs/MQTT.js/blob/main/.github/workflows/release-it.yml#L42)

[robertsLando]

@frenck @jmgiaever FYI after this will be released:

All backend files have been moved to api folder, this includes bin config hass lib and app.ts. In case HA addon or snap package could be broken by this change I inform you.

In future I would like to switch to a monorepo using lerna but that requires much more work and I'm not sure I want it yet...