Add support for payload_template in rest component

[ptashek]

Breaking change

Proposed change

This PR picks up where #73106 left off. This change adds the option to use templates in rest sensor payload option, allowing to send dynamically changed payloads to the remote endpoint. This is especially useful with APIs like GraphQL, as demonstrated in my comment on the feature request thread on the community forum.

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

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request: Update rest.markdown to include payload_template option home-assistant.io#30710

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
• 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.

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.
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[home-assistant]

Hi @ptashek

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[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

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Stale

[ptashek]

Related documentation update PR: home-assistant/home-assistant.io#30710

[luuuis]

Nice work.

[ptashek]

@luuuis Thank you for the review and the approval.
Not sure why the merge is still blocked - is there a specific maintainer that must approve additionally?

[luuuis]

I suppose so @ptashek , I am new and not sure of the process myself.

[IceBotYT]

Works for me!

[emontnemery]

This too needs the exclusive marker

[emontnemery]

LGTM, thanks @ptashek 👍

I'd like a second opinion before merge though

[emontnemery]

After looking at the missing code coverage I'm not so sure about the changes.
Also, the RestData class is shared with the scrape integration, does that integration need to be changed too when we make changes here?