Add `strptime`/`strftime` format code examples

[ezio-melotti]

Currently the docs for datetime.strptime and datetime.strftime don't include an example but have a link to the table with the format codes, where I end up having to reconstruct the right combination every time. At the end of each class docs there are some examples, but there are no links pointing to them, so they aren't easily discoverable. In addition, the .(from)isoformat methods can often be used instead of strftime/strptime.

I therefore suggest the following changes:

1. add an example before the table with the format codes, showing some of the most common codes;
2. add links to (date|time|datetime).isoformat in the docs for (date|time|datetime).strptime;
3. add links to datetime.fromisoformat in the docs for datetime.strptime (date and time have a .fromisoformat method, but no .strptime method);

Linked PRs

• gh-100574: add examples/links to the strptime/strftime docs #100575
• [3.11] gh-100574: add examples/links to the strptime/strftime docs (GH-100575) #103368

[hugovk]

Merged to main/3.12 and backported to 3.11. ✅