Do not change working directory to `_quarto.yml` directory

[machow]

Currently when running quartodoc build ... we change the working directory to be the one holding _quarto.yml. This is to support specifying a custom quartodoc renderer inside your quarto project. (see PRQL/pyprql#272)

One downside of this approach is that a user might be able to import their package from root (due to it being in the working directory), but not import it when we change the working directory to be a docs/ subfolder.

Let's append the docs/ subfoldersys.path instead. This has 2 advantages:

• anything in a docs/ subfolder will have least precedence when importing.
• behaviors that lean on the working directory being wherever quartodoc build ... was run from are preserved.

[machow]

Should be resolved in https://github.com/machow/quartodoc/releases/tag/v0.6.4.

I ended up keeping the behavior of changing directories, but quartodoc now appends the currently directory to the end of sys.path (so if you were depending on it to import anything, it should hopefully still work)