chore(functions/concepts-stateless): Update sample to use declarative signature (#9040)

Co-authored-by: Charles Engelke <[email protected]>

Author: Kenneth Rosario

functions/concepts-stateless/main.py

@@ -12,14 +12,15 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import time
+# [START functions_concepts_stateless]
+import functions_framework
 
 
-# [START functions_concepts_stateless]
 # Global variable, modified within the function by using the global keyword.
 count = 0
 
 
+@functions_framework.http
 def statelessness(request):
     """
     HTTP Cloud Function that counts how many times it is executed

functions/concepts-stateless/requirements-test.txt

@@ -1,2 +1,3 @@
 flask==2.1.0
 pytest==7.0.1
+functions-framework==3.3.0

functions/concepts-stateless/requirements.txt

@@ -0,0 +1 @@
+functions-framework==3.3.0