Research and implement (region) caching

[lhjohn]

Caching can reduce traffic and costs for the Academy and response time for users.

1. Check if OPcache is activated in our Moodle environment: https://docs.moodle.org/38/en/OPcache
2. AWS offers ElastiCache for Memcached. Check if this is interesting to us: https://aws.amazon.com/elasticache/memcached/
3. CloudFront is a content distribution network to cache for different regions. This may be interesting to implement, if regions such as Asia or US experience high latency with our Ireland server: https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/GettingStarted.html