Jira: https://jira.ez.no/browse/EZP-31350

Backport changes that happened since the adapters where proposed last winter, until it was accepted and improved further within Symfony codebase.

Benefits:

• Removes requirement for phpredis 3.1.3, which was an issue on platform.sh on PHP 7.1 and PHP 7.2 (currently needed with eZ Commerce for instance), and in some development environments compiled with older extension
• Logs message & refuses to save cache if Redis server has been configured with wrong eviction policy
• Should be able to handler larger cache pool, as cache clearing by tag is done in batches
  • Redis details for Tag Set usage: 1. Rename Set to be atomic 2. Read batch of keys 3. delete ➰ back to 2. till empty
• Now a almost pure backported Adapter, easier to maintain and works as polyfill for Symfony 4.4 with same namespace / class name

Cons:

• There were never tests for that here, but Predis with RedisCluster (as opposed to more common PredisCluster) support was dropped on symfony on the last changes around this, there might be someone using this with 2.5LTS so we might want to bump version number to 2.0 here and drop support for that in 2.5LTS doc. However it's rather strange to use Predis when you also have phpredis extension, our doc tries to imply a phpredis OR Predis. Ref: [Cache] Improve RedisTagAwareAdapter invalidation logic & requirements symfony/symfony#33461 (review)

TODO:

• Travis
• QA (including making sure this does not break 2.5 in anyway)