Add PHP Redis extension to all Docker images (apache, fpm, fpm-alpine)

[bwilhelm-gst]

What

This PR adds installation and runtime enablement of the PHP redis extension in all three Docker image variants in espocrm-docker:

• espocrm-docker/apache/Dockerfile
• espocrm-docker/fpm/Dockerfile
• espocrm-docker/fpm-alpine/Dockerfile

Why

Redis is required to support shared PHP sessions via session.save_handler=redis.

This is important for High Availability (HA) deployments of EspoCRM, where multiple application instances run behind a load balancer and must share session state consistently.

Changes

• Added pecl install redis during image build.
• Added redis to docker-php-ext-enable so the extension is loaded at runtime.

Validation

• Docker image build was executed successfully for the updated variant.
• Runtime extension check can be done with:
  • php -m | grep -i '^redis$'

Impact

• No application-level behavior change by default.
• Enables Redis-backed PHP session storage for HA/multi-node deployments.