Use UUID identifier in System Bridge

[timmo001]

Proposed change

Add UUID as identifier for System Bridge device

Type of change

• Code quality improvements to existing code or addition of tests

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 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.

The integration reached or maintains the following Integration Quality Scale:

• 🥈 Silver

To help with the load of incoming pull requests:

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

[frenck]

Just a quick question: Why not move this whole device info into the above SystemBridgeEntity and remove the SystemBridgeDeviceEntity altogether?

[timmo001]

Good point 👍

[Swamp-Ig]

LGTM

[frenck]

Thanks, @timmo001 👍