Docs: add HITL operators to Standard Provider operator index

[suii2210]

What does this PR do?

Adds documentation for HITL operators to the Standard Provider operator index,
making them discoverable alongside other operators.

Why is this needed?

HITL operators were only accessible via the Python API docs, which made them
hard to find from the provider documentation. This PR fixes that gap.

What is included?

• New hitl.rst page under Standard Provider operators
• Links to Python API reference and HITL tutorial
• Registration of HITL operators in the provider operator index

Closes #60614

[shahar1]

Currently static checks fail, and also @Lohith625 had asked to be assigned first to the original issue, and later created another PR handles more aspects (#60681).
In that case, I'd rather let them to finalize the PR and close this one - please feel free to review their work, and in the meanwhile you may ask to be assigned to other issues (there are plenty!). Specifically in the case of docs, you could also directly create a PR to fix existing problems that currently don't have GitHub issues.
To avoid clashes for the next time in resolving GitHub issues, please check first if someone has already asked to be assigned to the issue and give them the chance to handle it. If they have been inactive for a while (let's say - a week or so), then you may take over.