Add workflow for creating new releases

Whenever a release branch - that is a branch starting with `release/` -
is merged into master, we create a new GitHub release based on the
version number in the branch name.

Similarly to the preview release, we extract the relevant section of
the changelog and make it the release body.

.github/workflows/build-release-binaries.yml

@@ -1,12 +1,12 @@
-name: "Release swap and asb"
+name: "Build swap and asb release binaries"
 
 on:
   release:
     types: [created]
 
 jobs:
-  release:
-    name: Release swap
+  build_binaries:
+    name: Build swap and asb binaries
     strategy:
       matrix:
         include:

.github/workflows/create-release.yml

@@ -0,0 +1,41 @@
+name: "Create release"
+
+on:
+  pull_request:
+    types:
+      - closed
+
+jobs:
+  create_release:
+    name: Create from merged release branch
+    if: github.event.pull_request.merged == true && startsWith(github.event.pull_request.head.ref, 'release/')
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Extract version from branch name
+        id: extract-version
+        shell: python
+        run: |
+          branch_name = "${{ github.event.pull_request.head.ref }}"
+          version = branch_name.split("/")[1]
+
+          print(f"::set-output name=version::{version}")
+
+      - name: Extract changelog section for release
+        id: changelog
+        uses: coditory/changelog-parser@v1
+        with:
+          version: ${{ steps.extract-version.outputs.version }}
+
+      - name: Create release
+        uses: actions/create-release@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.BOTTY_GITHUB_TOKEN }}
+        with:
+          tag_name: ${{ steps.extract-version.outputs.version }}
+          release_name: ${{ steps.extract-version.outputs.version }}
+          draft: false
+          prerelease: false
+          body: ${{ steps.changelog.outputs.description }}
+          commitish: ${{ github.event.pull_request.merge_commit_sha }}