chore(ci): publish feature branches to edge/ (#1373)

This is pretty much a copy-paste of the equivalent yaml from Rockcraft.

Fixes #1372

.github/workflows/tests.yaml

@@ -2,7 +2,9 @@ name: Tests
 
 on:
   push:
-    branches: [ main ]
+    branches:
+      - main
+      - "feature/**"
 
   pull_request:
 
@@ -99,6 +101,24 @@ jobs:
         with:
           name: snap
           path: ${{ steps.snapcraft.outputs.snap }}
+      - name: Get branch name
+        id: vars
+        run: |
+          if [[ "${{ github.event_name }}" == "pull_request" ]]
+          then
+            echo "branch=pr-${{ github.event.number }}" >> "$GITHUB_OUTPUT"
+          else
+            branch=$(echo ${GITHUB_REF#refs/*/} | sed -e 's|feature/\(.*\)|\1|')
+            echo "branch=$branch" >> "$GITHUB_OUTPUT"
+          fi
+      - name: Publish feature branch to edge/${{ steps.vars.outputs.branch }}
+        if: ${{ env.SNAPCRAFT_STORE_CREDENTIALS != '' }}
+        uses: snapcore/action-publish@v1
+        env:
+          SNAPCRAFT_STORE_CREDENTIALS: ${{ secrets.SNAPCRAFT_STORE_CREDENTIALS }}
+        with:
+          snap: ${{ steps.snapcraft.outputs.snap }}
+          release: edge/${{ steps.vars.outputs.branch }}
 
 # Commented out until we can provide the necessary launchpad credentials.
 #  snap-remote-build: