CI/CircleCI: Authenticate to DockerHub when pulling the docker image (#25581)

For more information see the following links:
- https://www.docker.com/blog/scaling-docker-to-serve-millions-more-developers-network-egress/
- https://docs.docker.com/docker-hub/download-rate-limit/
- https://circleci.com/docs/2.0/private-images/

Add DOCKERHUB_USERNAME and DOCKERHUB_PASSWORD secrets to CircleCI Environment Variables. DOCKERHUB_PASSWORD can be either the password or an access token.

(cherry picked from commit e3da1ed245)

.circleci/config.yml

@@ -3,7 +3,13 @@ jobs:
   codestyle_and_sql:
     docker:
       - image: trinitycore/circle-ci:master-buildpacks-focal
+        auth:
+          username: $DOCKERHUB_USERNAME
+          password: $DOCKERHUB_PASSWORD
       - image: circleci/mysql:8
+        auth:
+          username: $DOCKERHUB_USERNAME
+          password: $DOCKERHUB_PASSWORD
         environment:
           MYSQL_ALLOW_EMPTY_PASSWORD: yes
           MYSQL_ROOT_PASSWORD: ''
@@ -39,6 +45,9 @@ jobs:
   pch:
     docker:
       - image: trinitycore/circle-ci:master-buildpacks-focal
+        auth:
+          username: $DOCKERHUB_USERNAME
+          password: $DOCKERHUB_PASSWORD
     steps:
       - run:
           name: Checkout
@@ -70,6 +79,9 @@ jobs:
   nopch:
     docker:
       - image: trinitycore/circle-ci:master-buildpacks-focal
+        auth:
+          username: $DOCKERHUB_USERNAME
+          password: $DOCKERHUB_PASSWORD
     steps:
       - run:
           name: Requirements