Rebuilt Splunk using custom library

[Bre77]

Proposed change

Changed the Splunk integration to use an external Pypi library, rather than requests. This indirectly has fixed a data formatting issue the previous version of this integration had, introduces batching to reduce the number of connections, and validates the Splunk Token on setup.

By design the integration will not fail if Splunk is down, as this can be expected when restarting a physical host that is running both Home Assistant and Splunk.

These fixes has previously been submitted as PR #39774 and #40015, reworked based on feedback from @MartinHjelmare

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:

No change from documentation at https://www.home-assistant.io/integrations/splunk/

Additional information

n/a

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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To help with the load of incoming pull requests:

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

[MartinHjelmare]

Looks good!