Enable Enphase Envoy authentication credentials update

[catsmanac]

Proposed change

Enphase Envoy integration currently reports device already exists when adding another integration for the same envoy serial-number as an existing one. There is no way to update the credentials or the IP address of the existing one other then removing/re-adding the integration.

This PR changes this behavior by updating the existing entry with the specified IP, username and password. In this way the stored credentials can be updated by adding another Enphase Envoy integration with desired IP, username and password. The identification is done on the Envoy serial-number which is the device unique_id. If these match, the existing interation entry is updated.

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: https://github.com/home-assistant/home-assistant.io/pull/31410

Checklist

• [x] The code change is tested and works locally.
• [x] Local tests pass. Your PR cannot be merged unless tests pass
• [x] There is no commented out code in this PR.
• [x] I have followed the development checklist
• [x] I have followed the perfect PR recommendations
• [x] The code has been formatted using Ruff (ruff format homeassistant tests)
• [x] Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• [x] Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• [ ] The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• [ ] New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• [ ] For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.
• [ ] Untested files have been added to .coveragerc.

To help with the load of incoming pull requests:

• [ ] I have reviewed two other open pull requests in this repository.

[home-assistant[bot]]

Hey there @bdraco, @cgarwood, @dgomes, @joostlek, mind taking a look at this pull request as it has been labeled with an integration (enphase_envoy) you are listed as a code owner for? Thanks!

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