Cabal project to compile docusaurus examples.

[Unisay]

Before this PR:

• docusaurus project contains Haskell source files that aren't typechecked and might contain compilation errors.
• A change in the Plutus plug-in or API might break examples without any CI failure.
• CIP-57 Example validator script isn't compatible with the CIP-69 and CIP-117.

After this PR:

• Cabal package docusaurus-examples exists to build a single executable example-cip57 (for now) which compiles a corresponding CIP-57 Blueprint example.
• A change in the Plutus plug-in or API that breaks examples will cause the whole project build to fail CI.
• CIP-57 Example validator script is compatible with the CIP-69 and CIP-117.