Add servant back to stackage

[arianvp]

https://github.com/commercialhaskell/stackage/blob/master/build-constraints.yaml#L1540

Now that everything builds with GHC 8.10 #1331 #1295 we should be able to re-add ourselves.

I do not know who controls that current mailing list that's in build-constraints. If the answer is that nobody does anymore than we should update it

[arianvp]

Probably needs #1334 too

[arianvp]

I asked around about the mailing list; but nobody responded. I suggest we create a new email address with the new maintainers; instead of trying to get hold of ownership of the old one.

[domenkozar]

I'd recommend https://github.com/haskell-servant/servant-auth/blob/master/.github/workflows/ci.yml

[arianvp]

Nice it seems a bit simpler than the haskell-ci stuff; which only seems to work with travis. I'll have a look

[domenkozar]

Yeah I find having CI abstraction in a releasable haskell package quite a feedback killer.

[serras]

I think with #1348 merged, you can now try to add it again to Stackage.

[maksbotan]

Done! Core packages, servant-blaze, servant-multipart and servant-swagger-ui are in nightly now: https://www.stackage.org/diff/nightly-2020-11-06/nightly-2020-11-08