[WIP] Replace instance of deprecated utcnow() and utcfromtimestamp()

[cat-bro]

For "Support Python 3.13 and Numpy 2" cofest topic with @nsoranzo

ref #16854

These functions will be deprecated with python 3.12 https://docs.python.org/3/whatsnew/3.12.html#deprecated

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[cat-bro]

this replacement is not equivalent. datetime.utcnow() is not timezone aware and what I have replaced it with is. I'll need to fix this.

[nsoranzo]

utcnow is also used in lib/galaxy/model/orm/now.py to define our own now function, which is then imported in a dozen files ($ ack --type=python 'galaxy.model.orm.now' to find them).

[jdavcs]

Converted to draft status due to WIP title edit. (that way it's easier to filter this out during release review).