Flip the default value of lukko flag in hackage-security

[Mikolaj]

Describe the feature request

Let's disable lukko by default on cabal master branch and if it works well, lets release cabal with this change and if it works well, let's make the flag flip also in hackage-security. Lukko is a workaround for a problem in base and it's hoped that it's not needed any more (and so it's not maintained as vigorously as when it was really needed).

Since cabal is the main (only?) user of https://github.com/haskell/hackage-security, let's discuss here (and not in hackage-security bug tracker) this course of action, initially proposed by @Bodigrim in haskellari/lukko#39 (comment). The ticket also provides the context for this change.

One of related cabal tickets suggests some users work with the proposed setup (no lukko) successfully for many years now: #6657

[fgaz]

Lukko is a workaround for a problem in base

Since it's dependent on base version we could change it to manual: False default: False. This way it will automatically turn on for old base versions (because of this bound).

Or if all problematic base versions are outside of our support window we can just (gradually, setting it to False first) drop it.

[Mikolaj]

We've agreed on the outline of the deprecation process, so with some luck it's a one-line change, but it requires grepping through the code to confirm the flag is not used in surprising ways and really not documented anywhere and, generally, some sanity checks and "what could go wrong" consideration.