Fix ONVIF config entry unique ID

[hunterjm]

Proposed change

Fixes issue where some ONVIF devices do not expose MAC address through the API. This falls back to the serial number as the config entry Unique ID, fixing #35883

While testing (adding and removing config entries after commenting out portions of code) I realized that the Event subscription is not ended properly when removing a config entry and will continue attempting to poll the device indefinitely until a Home Assistant reboot. A fix for that is also included in this PR.

While playing around in config flow, I also made password optional which fixes #35904

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)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example entry for configuration.yaml:

# Example configuration.yaml

Additional information

• This PR fixes or closes issue: fixes ONVIF integration error: "Could not configure unique ID for ONVIF device" #35883
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• 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
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

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.
• Untested files have been added to .coveragerc.

The integration reached or maintains the following Integration Quality Scale:

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[MartinHjelmare]

For the future, please separate different fixes into different PRs. That will speed up review and time to merge.

[hunterjm]

Will do RE more than one issue in this PR. The second issue really only changed the schema for one step changing a .Required to a .Optional, which is why it was included, and the event fix was isolated and 3 lines of code.

[MartinHjelmare]

Great!