Github Workflow migrations (#1574)

During the monorepo merge, the Github workflows for subtrate, polkadot
and cumulus were imported in various sub folders.
This PR merges and fixes some of those workflows and brings them back to
the root to make them available again.

---------

Co-authored-by: Egor_P <egor@parity.io>

.github/scripts/common/lib.sh

@@ -264,3 +264,41 @@ function check_gpg() {
     echo "Checking GPG Signature for $1"
     gpg --no-tty --verify -q $1.asc $1
 }
+
+# GITHUB_REF will typically be like:
+# - refs/heads/release-v1.2.3
+# - refs/heads/release-polkadot-v1.2.3-rc2
+# This function extracts the version
+function get_version_from_ghref() {
+  GITHUB_REF=$1
+  stripped=${GITHUB_REF#refs/heads/release-}
+  re="v([0-9]+\.[0-9]+\.[0-9]+)"
+  if [[ $stripped =~ $re ]]; then
+    echo ${BASH_REMATCH[0]};
+    return 0
+  else
+    return 1
+  fi
+}
+
+# Get latest rc tag based on the release version and product
+function get_latest_rc_tag() {
+  version=$1
+  product=$2
+
+  if [[ "$product" == "polkadot" ]]; then
+    last_rc=$(git tag -l "$version-rc*" | sort -V | tail -n 1)
+  elif [[ "$product" == "polkadot-parachain"  ]]; then
+    last_rc=$(git tag -l "polkadot-parachains-$version-rc*" | sort -V | tail -n 1)
+  fi
+  echo "${last_rc}"
+}
+
+# Increment rc tag number based on the value of a suffix of the current rc tag
+function increment_rc_tag() {
+  last_rc=$1
+
+  suffix=$(echo "$last_rc" | grep -Eo '[0-9]+$')
+  ((suffix++))
+  echo $suffix
+}