ci: add release workflows

[ianlewis]

• Add pull request check for building the Docker image
• Add release workflow to
  • build and push the Docker image
  • publish release binaries

The release steps are written in RELEASE.md. With immutable releases, the release cannot be updated after it is published. So we will use the following steps:

1. Create semver tag locally and push.
2. Release workflow is run automatically. A new draft release is created with attached binary, and a new Docker image is pushed.
3. Update the release description.
4. Publish the release (no changes possible after this point)

Fixes #8

[Copilot]

Pull request overview

This PR implements CI/CD workflows for building and releasing the project, including pull request checks and automated release publishing with immutable releases.

Changes:

• Added GitHub Actions workflows for Docker image builds on pull requests and releases
• Updated build configuration to support multi-architecture binary builds
• Documented the release process for using GitHub's immutable releases

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
RELEASE.md	Documents the release workflow process for immutable releases
Makefile	Updates build command to compile static binaries with platform-specific naming
Dockerfile	Updates Go version from 1.24 to 1.25
.github/workflows/release.publish.yml	Implements automated release workflow for building/publishing Docker images and binaries
.github/workflows/pull_request.build.yml	Adds PR check workflow for validating Docker image builds

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[ianlewis]

@Ladicle よろしくお願いします！

[Ladicle]

Overall, this looks great! Just one minor comment from my side!

[Ladicle]

I'm wondering if we need to upload binary files here. Other pfnet k8s-related repos only upload their container images. Most users use a container image directly. If needed, they can extract binaries from the container image.

[ianlewis]

Yeah, my thought was it would be easier to download the binary when using with other images as the base. But they could extract it from the container image using multi-stage builds.

In the case of ns-reloader, I think extracting it might actually be the most common use-case.

I'll go ahead and remove this, and we can add it back if needed later.