Automate publish (#339)

## Changes
Resolve #299

Rubygems provides a way to release gem with GitHub Actions officially.
It seems it doesn't require personal access token. let's try to use it.

On publishing, this workflow calls `bundle exec rake release`, and it
tries to push git tag. this doesn't match our use case. We always create
release note with git tag in this repository at first (in other 5 bot
sdk projects), and we want the workflow to publish(release) gem later.
This change modifies `release` task not to push git tag. I don't know if
this works. Let me try it.

ref:
- https://guides.rubygems.org/trusted-publishing/adding-a-publisher/ 
- I've set `publish.yml` in `line/line-bot-sdk-ruby` can be trusted in
`line-bot-api` gem:
https://rubygems.org/gems/line-bot-api/trusted_publishers
- https://github.com/rubygems/release-gem

.github/workflows/publish.yml

@@ -0,0 +1,38 @@
+name: Publish package to the RubyGems.org
+on:
+  release:
+    types: [published]
+  workflow_dispatch:
+    inputs:
+      version:
+        description: 'The version to release. v prefix is required (e.g. v1.10.0)'
+        required: true
+
+jobs:
+  push:
+    name: Push gem to RubyGems.org
+    runs-on: ubuntu-latest
+
+    permissions:
+      id-token: write # IMPORTANT: this permission is mandatory for trusted publishing
+      contents: write # IMPORTANT: this permission is required for `rake release` to push the release tag
+
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true
+          ruby-version: 3.3
+      - name: Update version file with the release version
+        run: |
+          if [ "${{ github.event_name }}" == "workflow_dispatch" ]; then
+            VERSION=${{ github.event.inputs.version }}
+          else
+            VERSION=${{ github.event.release.tag_name }}
+          fi
+          VERSION=${VERSION#v}
+
+          sed -i "s/VERSION = \".*\"/VERSION = \"$VERSION\"/" lib/line/bot/api/version.rb
+          
+          cat lib/line/bot/api/version.rb
+      - uses: rubygems/release-gem@v1

Rakefile

@@ -4,3 +4,13 @@ require 'rspec/core/rake_task'
 RSpec::Core::RakeTask.new(:spec)
 
 task default: :spec
+
+# We don't want to push tags to source control when releasing the gem
+Rake::Task["release"].clear
+
+# Redefine `release` task to build and push gem to RubyGems without pushing to source control
+## https://github.com/rubygems/bundler/blob/35be6d9a603084f719fec4f4028c18860def07f6/lib/bundler/gem_helper.rb#L53-L57
+desc "Build and push gem to RubyGems without pushing to source control"
+task "release", [:remote] => ["build", "release:guard_clean", "release:rubygem_push"] do
+  puts "Built and pushed gem to RubyGems without pushing to source control."
+end