Add short doc on how to create Aesara Ops for intermediate graph operations

[ricardoV94]

Follow up to #5538, we can probably remove the entire https://github.com/pymc-devs/pymc/blob/main/docs/source/Advanced_usage_of_Aesara_in_PyMC.rst

but we should perhaps keep the part about creating a new Aesara Op. We have pymc-examples that show how to create one Op for a Likelihood term (used inside a Potential), but not oneOp that would be used with the rest of the generative graph (and not only the logp graph). Users may not understand that possibility when reading the pymc-example guides.

[janeka1122]

Hi, wanted to know 2 things:

1. Can this issue be still worked upon.
2. Is the project part of the Hacktoberfest Program ?