Amazon S3 backup support

[lf-]

Uses amazonka-s3, which auto discovers credentials.

Did some manual testing:

glean --tier test --db-root ~/glean backup myrepo/0 s3:mybucket/jade-test
glean --tier test --db-root ~/glean2 restore s3:mybucket/jade-test/myrepo.0

Configuration ~/.config/glean/server/test, though I think this doesn't actually matter?

{
    "backup": {
        "allowed": ["myrepo"],
        "location": "s3:mybucket/jade-test"
    },
    "restore": {
        "enabled": true
    }
}

This feature really needs some documentation (especially given I don't know if fb expected anyone external to immediately go and use it so it's probably in a wiki somewhere?); I would appreciate the docs that exist getting released, or I can maybe write some.

[netlify]

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[lf-]

Plan: review internally with @parsonsmatt tomorrow then will mark as ready for review.

[lf-]

Reviewed with @parsonsmatt: we had some unsafePerformIO which existed to ensure that fromPath could get called multiple times while sharing the same lazily discovered AWS.Env (as those may require network access to create; they're kind of expensive), which I fixed by making adding backups an IO operation.

The goal here is that you can throw out the Backend object in client code and it won't really matter, and that AWS credentials are only discovered if the user is actually using the AWS features.

It's now in a state I'm happy with, so please take a look! :)

[simonmar]

This looks great! Thanks for the contribution.

[simonmar]

CI failure with 9.2.8

[lf-]

CI failure with 9.2.8

Fixed it :) Not surprised I got got by developing on the officially unsupported 9.10.x

[meta-codesync]

@aahanaggarwal has imported this pull request. If you are a Meta employee, you can view this in D93099368.