Add srtool GHA (#2755)

This PR introduces the `srtool` GHA which was used in the old `cumulus`
repo to build and check runtimes on the weekly basis schedule. The job
is triggered:
- every Monday at 2AM, automatically
- on each tag push or push to the release branch
- can be triggered manually as well

Addresses #1271

.github/scripts/common/lib.sh

@@ -307,3 +307,40 @@ function increment_rc_tag() {
   ((suffix++))
   echo $suffix
 }
+
+function relative_parent() {
+    echo "$1" | sed -E 's/(.*)\/(.*)\/\.\./\1/g'
+}
+
+# Find all the runtimes, it returns the result as JSON object, compatible to be
+# used as Github Workflow Matrix. This call is exposed by the `scan` command and can be used as:
+# podman run --rm -it -v /.../fellowship-runtimes:/build docker.io/chevdor/srtool:1.70.0-0.11.1 scan
+function find_runtimes() {
+    libs=($(git grep -I -r --cached --max-depth 20 --files-with-matches 'construct_runtime!' -- '*lib.rs'))
+    re=".*-runtime$"
+    JSON=$(jq --null-input '{ "include": [] }')
+
+    # EXCLUDED_RUNTIMES is a space separated list of runtime names (without the -runtime postfix)
+    # EXCLUDED_RUNTIMES=${EXCLUDED_RUNTIMES:-"substrate-test"}
+    IFS=' ' read -r -a exclusions <<< "$EXCLUDED_RUNTIMES"
+
+    for lib in "${libs[@]}"; do
+        crate_dir=$(dirname "$lib")
+        cargo_toml="$crate_dir/../Cargo.toml"
+
+        name=$(toml get -r $cargo_toml 'package.name')
+        chain=${name//-runtime/}
+
+        if [[ "$name" =~ $re ]] && ! [[ ${exclusions[@]} =~ $chain ]]; then
+            lib_dir=$(dirname "$lib")
+            runtime_dir=$(relative_parent "$lib_dir/..")
+            ITEM=$(jq --null-input \
+                --arg chain "$chain" \
+                --arg name "$name" \
+                --arg runtime_dir "$runtime_dir" \
+                '{ "chain": $chain, "crate": $name, "runtime_dir": $runtime_dir }')
+            JSON=$(echo $JSON | jq ".include += [$ITEM]")
+        fi
+    done
+    echo $JSON
+}