feat: Allow superset to be deployed under a prefixed URL (#30134)

Co-authored-by: Kamil Gabryjelski <kamil.gabryjelski@gmail.com>

.github/workflows/bashlib.sh

@@ -145,6 +145,7 @@ cypress-install() {
 
 cypress-run-all() {
   local USE_DASHBOARD=$1
+  local APP_ROOT=$2
   cd "$GITHUB_WORKSPACE/superset-frontend/cypress-base"
 
   # Start Flask and run it in background
@@ -152,7 +153,12 @@ cypress-run-all() {
   # so errors can print to stderr.
   local flasklog="${HOME}/flask.log"
   local port=8081
-  export CYPRESS_BASE_URL="http://localhost:${port}"
+  CYPRESS_BASE_URL="http://localhost:${port}"
+  if [ -n "$APP_ROOT" ]; then
+    export SUPERSET_APP_ROOT=$APP_ROOT
+    CYPRESS_BASE_URL=${CYPRESS_BASE_URL}${APP_ROOT}
+  fi
+  export CYPRESS_BASE_URL
 
   nohup flask run --no-debugger -p $port >"$flasklog" 2>&1 </dev/null &
   local flaskProcessId=$!