Misc Go container fixes

[cbrake]

This fixes the following issue:

 => ERROR [build 4/6] RUN go mod download && go mod verify                                                                         3.2s 
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 > [build 4/6] RUN go mod download && go mod verify:                                                                                    
0.554 go: go.mod requires go >= 1.21.3 (running go 1.21.1; GOTOOLCHAIN=local)                                                           
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Dockerfile:6                                                                                                                            
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   4 |                                                                                                                                  
   5 |     COPY go.mod go.sum ./                                                                                                        
   6 | >>> RUN go mod download && go mod verify                                                                                         
   7 |                                                                                                                                  
   8 |     COPY . ./                                                                                                                    
--------------------                                                                                                                    
ERROR: failed to solve: process "/bin/sh -c go mod download && go mod verify" did not complete successfully: exit code: 1               
build image: exit status 1                                                                                                

[cbrake]

Also added a fix for trying to run jetstream/api-migration/go

 => ERROR [build 6/6] RUN go build -v -o /app ./...                                                                                0.4s 
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 > [build 6/6] RUN go build -v -o /app ./...:                                                                                           
0.359 /go/pkg/mod/github.com/nats-io/nats.go@v1.31.0/jetstream/stream_config.go:22:2: missing go.sum entry for module providing package golang.org/x/text/cases (imported by github.com/nats-io/nats.go/jetstream); to add:
0.359   go get github.com/nats-io/nats.go/jetstream@v1.31.0                                                                             
0.359 /go/pkg/mod/github.com/nats-io/nats.go@v1.31.0/jetstream/stream_config.go:23:2: missing go.sum entry for module providing package golang.org/x/text/language (imported by github.com/nats-io/nats.go/jetstream); to add:
0.359   go get github.com/nats-io/nats.go/jetstream@v1.31.0                                                                             
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Dockerfile:9                                                                                                                            
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   7 |                                                                                                                                  
   8 |     COPY . ./                                                                                                                    
   9 | >>> RUN go build -v -o /app ./...                                                                                                
  10 |                                                                                                                                  
  11 |     FROM alpine                                                                                                                  
--------------------                                                                                                                    
ERROR: failed to solve: process "/bin/sh -c go build -v -o /app ./..." did not complete successfully: exit code: 1                      

[cbrake]

I'm probably missing something here as the example obviously ran for the nbe website ...