Upgrade compiler tooling and libraries.

[vikt0r0]

Purpose

Upgrade stackage snapshot to lts-20.4 and ghc to 9.2.5.

Changes

• Bump resolverin stack.yaml and fix build errors and warnings.
• Update dependencies on http2-client and http2-grpc-haskell to ones that are updated to support lts-20.4.

Depends on

Concordium/concordium-client#196
Concordium/http2-grpc-haskell#3
Concordium/http2-client#3

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

[abizjak]

Looks good, but should wait for the dependencies to be merged before.

Please make a checklist in the PR description so it is easier to keep track of that.