feat: support configuring the manifold URL

[lf-]

I have a highly trivial Manifold implementation internally at Mercury for which I would like to set up for buck2 to receive rage and all that at. This allows for fully implementing the build logs feature mentioned in #441.

There's still a buck2_core::facebook_only() or two that need removed and some more tidying.

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[iguridi]

This is neat, taking a look

[iguridi]

One thing missing here is that it won't work when downloading logs via --trace-id .

Probably the way forward on that is to actually use our ManifoldClient there instead of relying on shelling out. Having said that, this PR should still work for rage and html, so if you just want to add a TODO there and do it in a different PR that is ok with me

added a couple of nits, feel free to ignore those for now

[lf-]

One thing missing here is that it won't work when downloading logs via --trace-id .

It actually does work for this, but only because I simply implemented the curl URL structure in locally-euclidean. It is a little goofy but it works.

How would you like to proceed with fixing this after landing this PR though? Should buck2 just fetch them from the fbcdn (and equivalent) URLs in ManifoldClient? Should it implement the actual Manifold GET API (in which case I can't help you because I don't know what it is)?

[lf-]

Looks like a bogus CI failure (or at least one I have nothing to do with). Surprised it builds internally at Facebook given that I suspect I broke a usage of the API I replaced (ManifoldClient::new), but shrug! Whatever works!