2.1.8" Add igbinary and redis PHP extensions

[defunctl]

Main Changes

• Our built images are missing the PHP Redis extension.
• igbinary is a compact, high-performance binary serializer which can reduce Redis memory usage by ~50%.

I built PHP 7.4 versions locally:

$ docker run --rm --entrypoint php slic-wp-redis-test -i | grep -i redis
/usr/local/etc/php/conf.d/docker-php-ext-redis.ini,
redis
Redis Support => enabled
Redis Version => 6.3.0
Redis Sentinel Version => 1.0
redis.arrays.algorithm => no value => no value
redis.arrays.auth => no value => no value
redis.arrays.autorehash => 0 => 0
redis.arrays.connecttimeout => 0 => 0
redis.arrays.consistent => 0 => 0
redis.arrays.distributor => no value => no value
redis.arrays.functions => no value => no value
redis.arrays.hosts => no value => no value
redis.arrays.index => 0 => 0
redis.arrays.lazyconnect => 0 => 0
redis.arrays.names => no value => no value
redis.arrays.pconnect => 0 => 0
redis.arrays.previous => no value => no value
redis.arrays.readtimeout => 0 => 0
redis.arrays.retryinterval => 0 => 0
redis.clusters.auth => no value => no value
redis.clusters.cache_slots => 0 => 0
redis.clusters.persistent => 0 => 0
redis.clusters.read_timeout => 0 => 0
redis.clusters.seeds => no value => no value
redis.clusters.timeout => 0 => 0
redis.pconnect.connection_limit => 0 => 0
redis.pconnect.echo_check_liveness => 1 => 1
redis.pconnect.pool_detect_dirty => 0 => 0
redis.pconnect.pool_pattern => no value => no value
redis.pconnect.pool_poll_timeout => 0 => 0
redis.pconnect.pooling_enabled => 1 => 1
redis.session.compression => none => none
redis.session.compression_level => 3 => 3
redis.session.early_refresh => 0 => 0
redis.session.lock_expire => 0 => 0
redis.session.lock_failure_readonly => 0 => 0
redis.session.lock_retries => 100 => 100
redis.session.lock_wait_time => 20000 => 20000
redis.session.locking_enabled => 0 => 0
Registered save handlers => files user redis rediscluster 
This program is free software; you can redistribute it and/or modify