Support named releases: lts

[maleadt]

Doesn't work right now: https://buildkite.com/julialang/stochasticdiffeq-dot-jl/builds/692#0192e3b3-2c2e-4a01-ad6c-74b2d8c1841b

[Krastanov]

Support for "alpha" (not just "nightly") would be great too