[nabil1440]

Change

• A Makefile adds these targets: build, test, vet, lint, vuln, fmt, fmt-check, check, release, clean and help. The targets follow the migration-agent repository.
• make build makes bin/fly with the version, the commit and the date from git.
• make lint and make vuln run fixed tool versions through go run. Thus Go builds the tools with the Go version of this module.
• make check runs fmt-check, vet, lint, test and vuln. It is the local gate before each merge, because the team skipped enhancement(ci): add checks for pull requests and replace the archived release actions #7.
• make release makes the static linux/amd64 and linux/arm64 archives and build/checksums.txt. VERSION replaces the version from git.
• build.sh is now a wrapper for make release. Thus the release workflow does not change.
• The README documents the targets.

Caution

CAUTION: DO NOT CHANGE THE NAMES OR THE CONTENTS OF THE RELEASE ASSETS. IF YOU CHANGE THEM, THE INSTALLED CLIS CANNOT RUN fly update.

• make release makes the same archive names and contents as the build.sh before this PR.

Tests

• make release VERSION=v9.9.9 on macOS (GNU Make 3.81):
  • The archive names and entries are the same as the output of the old build.sh. The files in build/ are also the same.
  • shasum -c checksums.txt passes.
  • file shows two static, stripped binaries.
  • The arm64 binary shows fly-cli version v9.9.9.
• ./build.sh in a golang:1.27 linux/amd64 container (GNU Make 4.4.1) makes static binaries, and the checksums agree.
• make build: bin/fly version shows the git version.
• make check passes: 0 lint issues, all tests pass, no vulnerabilities.
• make fmt-check fails when a file is not formatted.

Closes #16