⬆️ Bump Go 1.19 + `gearbox` 1.2 + set `GOAMD64=v3`

[0uep]

• Bump gearbox from v1.1.1 to v1.2.4
• Bump Go from 1.14 to 1.19: Each Go version improves the performance.
• Set GOAMD64=v3 to enable the following instructions set: CMPXCHG16B, LAHF, SAHF, POPCNT, SSE3, SSE4.1, SSE4.2, SSSE3, AVX, AVX2, BMI1, BMI2, F16C, FMA, LZCNT, MOVBE, OSXSAVE. The default value is GOAMD64=v1. See https://github.com/golang/go/wiki/MinimumRequirements#amd64
• Replace the RUN go get -u github.com/valyala/quicktemplate/qtc (Dockerfile) by //go:generate go run github.com/valyala/quicktemplate/qtc in the source code. That way Go-1.19 is aware of the dependency on qtc and adds automatically it in the go.mod with a fixed version to reproduce the same go generate.
• Rename module name from gearbox/src to gearbox/app. This change sets the default executable name to "app". We may also drop the -o app in the Dockerfile.

Note: I insert docker.io/ in the FROM docker.io/golang:1.19 statement to allow podman and buildah to build the container images.