fix: move examples_to_skip from docs/examples/conftest.py to the new marker system

[jakelorocco]

Prior to enabling markers for the examples, we had a variable called examples_to_skip that would skip collecting certain files from the docs/examples folder. We should migrate those examples to the commented marker system.

As a part of this, we should ensure which files should actually be skipped. There were a few that shared names with other files in the directory (ie __init__.py). We should prioritize running those that can be run (even if they are overly simple like the non-failing __init__.pys).

[jakelorocco]

If this also results in the skipped tests as being output as "skipped", we should remove the pytest_terminal_summary function from the conftest file as well since it will be duplicate information.

[AngeloDanducci]

I'll take a look at this one.