Allow manual scan and add delay in modbus switch verify

[janiversen]

Breaking change

Proposed change

setting scan_interval: 0, disables the timer, and thus there are no polling. This feature is useful for switches, where there are no physical contact and therefore no reason to poll.

Add new parameter:

modbus:
    ...
    switches:
        - name: test1
           verify:
              delay: 10

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

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:
  New parameter "delay" in modbus switch.verify home-assistant.io#17930

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.

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To help with the load of incoming pull requests:

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

[probot-home-assistant]

Hey there @adamchengtkc, @vzahradnik, mind taking a look at this pull request as its been labeled with an integration (modbus) you are listed as a codeowner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[janiversen]

@thehaxxa this one is for you.

[janiversen]

@MartinHjelmare thanks for reviewing my 2 other PRs, the change in this PR is more important since 2021.6 is cut this Wednesday and this is a schema change.

[MartinHjelmare]

Looks good!