feat: set config in environment vars/config files

[NickCrews]

Originally posted by @lboller-pwbm in #10231 (comment)

It would be sometimes nice to be able to avoid boilerplate of configuring ibis for every notebook/script. I for instance have this in my machine-wide settings for vscode to run on startup of every jupyter notebook:

    "jupyter.runStartupCommands": [
        "%load_ext autoreload",
        "%autoreload 2",
        "import contextlib",
        "with contextlib.suppress(ImportError): import ibis; ibis.options.interactive=True; ibis.Expr.to_sql = lambda self: ibis.to_sql(self); ibis.Expr.psql = lambda self: print(ibis.to_sql(self))",
        "with contextlib.suppress(ImportError): from ibis_widget import install; install()",
    ],

I see a few options on how to do this:

1. environment variables
2. local config files, eg searching up the dir tree eg ./ibis.toml, ../ibis.toml, ../../ibis.toml, etc
3. user/machine-wide config, eg ~/.config/ibis/config.toml

I think if it's not quite easy to do this, then it's not worth it. But I wanted to have an issue/discussion for this. Feel free to convert to discussion or close this.

[gforsyth]

I definitely agree that this is a good feature to have -- one of the reasons that from ibis.interactive import * is a thing is to scratch this same itch, but with a project that works with so many backends, I think we need to make the knobs customizable to all users.

I've spent way more time than I care to think about on problems like this -- here is my general outline of things that we could/should do and the order to do them in (roughly). It's ok to bail out at any point along here, including at step 0.

1. Support user-level configuration in XDG style directories (I have a reference somewhere for where Windows likes to store these files, so we can be OS-specific).
2. Add in a option in Ibis to disable all config files, because once we introduce hidden state, bug reports get harder to reproduce. So we'll need an easy-to-follow setup for "without any customization, this thing broke in this way"
3. Per-project/per directory config files. These should supersede any options set in the user-level config file (via a dictionary merge or similar)
4. Environment variables. I would strongly suggest avoiding these because env-variables are effectively entries in a single global configuration file that ALL installed software shares. If we do go down this path, all environment variables should be prepended with IBIS_ because there will be name collisions and unwinding them sucks.

[NickCrews]

I think uv probably has things to teach us about how to do configuration. I like how they do it. I think they do everything at the rust level though, so I don't think we can take advantage of it :(

spaCy uses confection, which looks simple and interesting.