feat: make ftl build et al work with Go

[alecthomas]

• ftl-go has been deleted.
• There must be a 1:1 mapping between FTL modules and Go modules.
• Updated ftl init go to generate a valid module.
• Updated all of the Go examples, including online-boutique, which can now be trivially started with ftl dev ./examples/online-boutique
• The tooling is quite restrictive about code layout at the moment, but we can come back to that later.

eg. Create, deploy and call a new module.

🐚 ~/dev/ftl $ ftl init go examples echo2
info: Initializing FTL Go module echo2 in examples
info: Running go mod tidy
🐚 ~/dev/ftl $ ftl deploy examples/echo2
info: Creating deployment for module echo2
info: Building Go module 'echo2'
info: Generating external modules
info: Extracting schema
info: Generating main module
info: Compiling
info: Uploading 1/1 files
info: Uploaded examples/echo2/_ftl/main as ba6f7f20ee5dac4e97197633348b5bb41e68e63c7e2d9b1da614d0a011b83872:main
info: Created deployment echo2-0a1cebbfcc
🐚 ~/dev/ftl $ ftl call echo2.echo
{"message":"Hello, anonymous!"}