Improve Growatt Server config flow with region dropdown

[johanzander]

Proposed change

1. Replace raw server URLs with user-friendly region names in both password and token authentication flows. This improves the user experience by showing clear region names instead of technical URLs in the dropdown selector.
2. Update URL/regions to be aligned with both official Growatt and Home Assistant documentation: https://www.home-assistant.io/integrations/growatt_server/

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• 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

Technical changes:

• Converted SERVER_URLS list to SERVER_URLS_NAMES dictionary mapping region keys to URLs
• Added missing Era/Atess Power server option that was documented but not available
• Implemented SelectSelector with translation_key="region" for proper localization
• Added server region selection to token authentication (previously missing)
• Updated tests to include CONF_URL in token authentication fixture
• Marks docs-configuration-parameters quality scale rule as done (Silver tier)

Checklist

• I understand the code I am submitting and can explain how it works.
• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• I have followed the perfect PR recommendations
• The code has been formatted using Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.
• Any generated code has been carefully reviewed for correctness and compliance with project standards.

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

• 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.

N/A - No dependency changes for this PR.

To help with the load of incoming pull requests:

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