Unstable documentation proof of concept

[bugadani]

Closes #2498

[MabezDev]

Looks good! How do we want to go about landing this?

We could mark all the modules we're not actively trying to stabilize in this PR, and then for the modules we are trying to stabilize we add the analysis issue link to each? Alternatively we could leave the 4 drivers we're trying to stabilize alone in this PR and follow up with the outcome from the analysis issues.

[MabezDev]

I guess the third option is don't mark anything yet, but just merge this as the prior construction work

[bugadani]

As this PR doesn't address #2499 I don't think I should mark anything unstable :) But:

• for one, I want to add the matching not_actually_docsrs to esp-wifi, so that we don't lose the banner there
• we might want to default-enable unstable for now, just to make our lives easier. We can then incrementally add the unstable gates as we see fit.

[bugadani]

I guess I should at least changelog the new feature, but maybe also start writing the migration guide as well. I don't think we need anything fancy, but this will need to be mentioned.

[jessebraham]

LGTM

[playfulFence]

LGTM, thanks!
It will take some amount of work to label all such things, but PoC is successful IMO.