Enable docker builds with shell using different dockerfile

[SamMorrowDrums]

As a first step to enabling shell access in our Docker image for developers that wish to use an image with a distro, this adds Dockerfile-with-shell to the repository root and can be run like so:

docker build --file  Dockerfile-with-shell . --tag ghcr.io/github/github-mcp-server:sh 
docker run --rm -it --entrypoint /bin/sh ghcr.io/github/github-mcp-server:sh 

In future we could consider letting this be a later build stage in our main Dockerfile and for our releases use the specific distroless build stage, while enabling others to build with a distro by default which is more common.

Motivation: #574
Docker's custom override: dgageot@2e73e0a
The Docker MCP Hub listing that points to unsanctioned (by GitHub) fork: https://hub.docker.com/r/mcp/github-mcp-server

CC @dgageot

[Copilot]

Pull Request Overview

Adds a new multi-stage Dockerfile to support interactive shell access for developers by building the Go server on Alpine and producing a shell-enabled runtime image.

• Introduces Dockerfile-with-shell with a build stage (including Git and Go caching) and a runtime stage with ca-certificates.
• Provides default ENTRYPOINT and CMD for running the compiled server.
• Enables developers to build and run the image with /bin/sh for distro-based debugging.

Comments suppressed due to low confidence (1)

Dockerfile-with-shell:1

• Consider adding updates to the project README (or a docs file) with instructions on how to build and run this new Dockerfile (e.g., docker build -f Dockerfile-with-shell . -t <tag> and the recommended docker run flags) so developers can discover and use it easily.

FROM golang:1.24.4-alpine AS build

[Copilot]

[nitpick] To improve clarity and allow targeted builds, you might name the runtime stage (e.g., FROM alpine:3.21 AS runtime) so consumers can explicitly reference it when building or inspecting images.

Suggested change

	FROM alpine:3.21
	FROM alpine:3.21 AS runtime