docs: add logo, dark mode, boost search

[ion-elgreco]

• Adds transparent logo (we need a higher quality one), I've pinged @fvaleye on Slack to check whether he has one.
• Add dark mode toggle
• Boost some search results since it was prioritizing the guides over the API reference

[roeap]

if the logo is transparent, should we use it in the README as well?

w.r.t. boosting API reference, depending on the audience, the examples might be more helpful? maybe @MrPowers has an opinion?

[MrPowers]

LGTM, but not sure about the search boosting... My guess is that we want the usage/integration pages ranked above the API docs (and the usage pages linking to the API docs). Open to thoughts. Normally I don't think API docs give the best SEO experience.

[ion-elgreco]

@roeap let's wait on a higher quality version of the transparent logo from Florian. This one I made myself with paint 3d but the edges are quite rough and the resolution got lower because of that.

@MrPowers I personally prefer the API reference to hit first in the search box. For example, I was looking for write_deltalake. The first 10 hits were all the guides, only the last one was the actual API reference.

So now with the boosting, the API reference will be first and then all the guides.

[roeap]

@dennyglee made me aware of the assets available in the delta-docs repo. Maybe we should use these? There are high quality PNGs as well as SVG versions available.

[ion-elgreco]

Awesome @roeap @dennyglee! That was what I was looking for :D

[roeap]

Looking great!

Re the boosting stuff, since API reference returns much fewer results, I guess the guides will still be visible on the result set - in contrast to the other way around.