Restore old docs and workflow

[PabloAndresCQ]

Description

There's some problems with the new version of docs (listed in the linked issue). As such, for now pytket-cutensornet will continue maintaining the old version of the docs, and using it as the main version. Once these issues are solved, I'm happy to make another release switching to the new docs.

Related issues

#139

Checklist

• I have run the tests on a device with GPUs.
• I have performed a self-review of my code.
• I have commented hard-to-understand parts of my code.
• I have made corresponding changes to the public API documentation.
• I have added tests that prove my fix is effective or that my feature works.
• I have updated the changelog with any user-facing changes.

[cqc-melf]

You would also need to remove the link to the new docs from the tket repo and update that to the old link as well.

[cqc-melf]

(see https://raw.githubusercontent.com/CQCL/tket/main/pytket/docs/extensions.rst )