1. Due to EZP-20324, legacy will clear SPI (may be stored in redis) cache when clearing content-view cache (./bin/console ezpublish:legacy:script - bin/php/ezcache.php --clear-id=content and when clearing cache from legacy admin)
2. Due to EZP-21321, SPI cache will be cleared when using symfony's clear:cache script (bin/console c:c

This is not always desirable:

• Running flushdb in a big redis cluster can be problematic ( https://github.com/redis/redis/issues/2691)
• On high-traffic sites you want to be careful about clearing SPI cache
• It is inconsistant that `clear:cache` suddenly starts to clear SPI cache once legacy-bridge is enabled.

Therefore, both behavior 1. and 2. should be configurable