chore: add releaser actions

[gaius-qi]

This pull request introduces a new release workflow and adds configurations for the modctl command-line tool, including its build and documentation process.

Release Workflow:

• Added a new GitHub Actions workflow for releases, which includes steps for checking out the repository, setting up Go, checking the GoReleaser configuration, and running GoReleaser. The workflow also generates a subject and sets tag output.

GoReleaser Configuration:

• Configured GoReleaser to create draft releases, download Go modules before building, and define builds for different operating systems and architectures. It also specifies the archive format and includes a checksum file.

Build and Documentation:

• Added a new Makefile target to generate the modctl man page using Pandoc.
• Added the generated modctl man page file (modctl.1) with detailed command usage and options.
• Added the source markdown file (modctl.1.md) for the modctl man page, which includes the same detailed command usage and options.

[chlins]

lgtm