Solve the "examples" problem

[alecthomas]

Examples in the FTL repo get out of sync because they're not tested. The problem is that if they were tested that would increase the burden on us, because we'd need to synchronously fix all examples on every commit.

Going with option 1 below.

• Upgrade FTL in ftl-examples and fix code (fix: upgrade deps and fix examples TBD54566975/ftl-examples#18)
• Reorganize examples so that online-boutique code is under a top level subfolder (chore: colocate online boutique files TBD54566975/ftl-examples#19)
• Remove unnecessary examples from ftl repo (chore: remove duplicate examples that moved to ftl-examples repo #937)
• Add go/kotlin folders to show language specific examples (Add go and kotlin examples TBD54566975/ftl-examples#20)

A couple of options we've discussed before:

1. Move all examples to https://github.com/TBD54566975/ftl-examples/. This will use a pinned version of FTL which we'll periodically upgrade. We'd still need some testing here but it would remove the burden of keeping the examples up to date synchronously with the rest of FTL.
2. Move all examples back into FTL and test them in CI.