Add gitlab job for publishing draft releases (#5009)

Idea is much the same as we currently do on polkadot - When a new tag is pushed (that fits our pattern for tags, e.g. v1.2.3), find a list of labelled changes and generate a changelog based on that. Create a draft release on Github and post about it on Matrix.

substrate/scripts/gitlab/publish_draft_release.sh

@@ -0,0 +1,95 @@
+#!/usr/bin/env bash
+
+# shellcheck source=lib.sh
+source "$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )/lib.sh"
+
+# Substrate labels for PRs we want to include in the release notes
+labels=(
+  'B1-runtimenoteworthy'
+  'B1-clientnoteworthy'
+  'B1-apinoteworthy'
+)
+
+version="$CI_COMMIT_TAG"
+last_version=$(git tag -l | sort -V | grep -B 1 -x "$version" | head -n 1)
+echo "[+] Version: $version; Previous version: $last_version"
+
+# Check that a signed tag exists on github for this version
+echo '[+] Checking tag has been signed'
+#check_tag "paritytech/substrate" "$version"
+case $? in
+  0) echo '[+] Tag found and has been signed'
+    ;;
+  1) echo '[!] Tag found but has not been signed. Aborting release.'; exit 1
+    ;;
+  2) echo '[!] Tag not found. Aborting release.'; exit
+esac
+
+all_changes="$(sanitised_git_logs "$last_version" "$version")"
+labelled_changes=""
+echo "[+] Iterating through $(wc -l <<< "$all_changes") changes to find labelled PRs"
+while IFS= read -r line; do
+  pr_id=$(echo "$line" | sed -E 's/.*#([0-9]+)\)$/\1/')
+
+  # Skip if the PR has the silent label - this allows us to skip a few requests
+  if has_label 'paritytech/substrate' "$pr_id" 'B0-silent'; then
+    continue
+  fi
+  for label in "${labels[@]}"; do
+    if has_label 'paritytech/substrate' "$pr_id" "$label"; then
+      labelled_changes="$labelled_changes
+$line"
+    fi
+  done
+done <<< "$all_changes"
+
+
+release_text="Substrate $version
+-----------------
+$labelled_changes"
+
+echo "[+] Release text generated: "
+echo "$release_text"
+exit
+echo "[+] Pushing release to github"
+# Create release on github
+release_name="Substrate $version"
+data=$(jq -Rs --arg version "$version" \
+  --arg release_name "$release_name" \
+  --arg release_text "$release_text" \
+'{
+  "tag_name": $version,
+  "target_commitish": "master",
+  "name": $release_name,
+  "body": $release_text,
+  "draft": true,
+  "prerelease": false
+}' < /dev/null)
+
+out=$(curl -s -X POST --data "$data" -H "Authorization: token $GITHUB_RELEASE_TOKEN" "$api_base/paritytech/substrate/releases")
+
+html_url=$(echo "$out" | jq -r .html_url)
+
+if [ "$html_url" == "null" ]
+then
+  echo "[!] Something went wrong posting:"
+  echo "$out"
+else
+  echo "[+] Release draft created: $html_url"
+fi
+
+echo '[+] Sending draft release URL to Matrix'
+
+msg_body=$(cat <<EOF
+**Release pipeline for Substrate $version complete.**
+Draft release created: $html_url
+EOF
+)
+formatted_msg_body=$(cat <<EOF
+<strong>Release pipeline for Substrate $version complete.</strong><br />
+Draft release created: $html_url
+EOF
+)
+send_message "$(structure_message "$msg_body" "$formatted_msg_body")" "$MATRIX_ACCESS_TOKEN"
+
+echo "[+] Done! Maybe the release worked..."