DOC: use autosummary on tensors.rst (#55042)
Summary:
Related to https://github.com/pytorch/pytorch/issues/52256
Splits tensors into a table-of-contents page and many sub-pages, one for each function
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55042
Reviewed By: mrshenli
Differential Revision: D27628688
Pulled By: zou3519
fbshipit-source-id: 08e87700a8e7d5b3fba3f1949e29e988a42bf2c6
