chore: updates the server startup

[lesterli]

Summary

This PR updates the server startup:

• start the http server in a goroutine, b/c httpServer.ListenAndServe() would block until shutdown
• move the shutdown handling to RunUntilShutdown
• replace WaitGroup to use channel

Test Plan

tested with the updated op test manager codes:

// create finality gadget
fg, err := finalitygadget.NewFinalityGadget(&fgCfg, fgDb, logger)
require.NoError(t, err)

// start finality gadget server
srv := fgsrv.NewFinalityGadgetServer(&fgCfg, fgDb, fg, shutdownInterceptor, logger)
go func() {
	err = srv.RunUntilShutdown()
	require.NoError(t, err)
}()

the logs:

INFO    server/server.go:91     gRPC server listening   {"address": "127.0.0.1:50051"}
INFO    server/server.go:120    Starting standalone HTTP server {"address": "127.0.0.1:8080"}
INFO    server/server.go:71     Finality gadget is active

[bap2pecs]

why replace WaitGroup to use channel?

also why is the channel name ready?

[lesterli]

WaitGroup only signals goroutine started, not if server is ready to accept connections, "ready" is used b/c it is clear for the channel's purpose

[bap2pecs]

WaitGroup only signals goroutine started, not if server is ready to accept connections

but how does it work in the past? we have always been using wg

"ready" is used b/c it is clear for the channel's purpose

ask Cursor. it's not a good name

[lesterli]

how does it work in the past?

right, WaitGroup works in server setups, but my understanding is the key difference is channels can propagate info while WaitGroup can only signal completion

it's not a good name

yes, it is too generic, maybe listenerReady is better name