feat(web-app-gitea): add optional Redis integration for caching, sessions, and queues

This update introduces conditional Redis support for Gitea, allowing connection
to either a local or centralized Redis instance depending on configuration.
Includes resource limits for the Redis service and corresponding environment
variables for cache, session, and queue backends.

Reference: ChatGPT conversation on centralized vs per-app Redis architecture (2025-10-15).
https://chatgpt.com/share/68ef5930-49c8-800f-b6b8-069e6fefda01

roles/web-app-gitea/vars/main.yml

@@ -22,9 +22,13 @@ GITEA_LDAP_AUTH_ARGS:
   - '--email-attribute "{{ LDAP.USER.ATTRIBUTES.MAIL }}"'
   - '--public-ssh-key-attribute "{{ LDAP.USER.ATTRIBUTES.SSH_PUBLIC_KEY }}"'
   - '--synchronize-users'
-GITEA_VERSION:    "{{ applications | get_app_conf(application_id, 'docker.services.gitea.version') }}"
-GITEA_IMAGE:      "{{ applications | get_app_conf(application_id, 'docker.services.gitea.image') }}"
-GITEA_CONTAINER:  "{{ applications | get_app_conf(application_id, 'docker.services.gitea.name') }}"
-GITEA_VOLUME:     "{{ applications | get_app_conf(application_id, 'docker.volumes.data') }}"
-GITEA_USER:       "git"
-GITEA_CONFIG:     "/data/gitea/conf/app.ini"
+GITEA_VERSION:        "{{ applications | get_app_conf(application_id, 'docker.services.gitea.version') }}"
+GITEA_IMAGE:          "{{ applications | get_app_conf(application_id, 'docker.services.gitea.image') }}"
+GITEA_CONTAINER:      "{{ applications | get_app_conf(application_id, 'docker.services.gitea.name') }}"
+GITEA_VOLUME:         "{{ applications | get_app_conf(application_id, 'docker.volumes.data') }}"
+GITEA_USER:           "git"
+GITEA_CONFIG:         "/data/gitea/conf/app.ini"
+
+## Redis
+GITEA_REDIS_ENABLED:  "{{ applications | get_app_conf(application_id, 'docker.services.redis.enabled') }}"
+GITEA_REDIS_ADDRESS:  "redis:6379"