Add vars to Synapse main.yml to control cache related config

This commit adds various cache related vars to main.yml for Synapse.

Some are auto tune and some are just adding explicit ways to control upstream vars.

roles/custom/matrix-synapse/defaults/main.yml

@@ -546,8 +546,17 @@ matrix_synapse_event_cache_size: "100K"
 
 # Controls cache sizes for Synapse.
 # Raise this to increase cache sizes or lower it to potentially lower memory use.
-# To learn more, see: https://github.com/matrix-org/synapse/issues/3939
-matrix_synapse_caches_global_factor: 0.5
+# To learn more, see:
+# - https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#caching
+# - https://github.com/element-hq/synapse#help-synapse-eats-all-my-ram
+# - https://github.com/element-hq/synapse/issues/3939
+matrix_synapse_caches_global_factor: 10
+matrix_synapse_caches_expire_caches: true
+matrix_synapse_caches_cache_entry_ttl: 30m
+matrix_synapse_caches_sync_response_cache_duration: 2m
+matrix_synapse_caches_autotuning_max_cache_memory_usage: 1024M
+matrix_synapse_caches_autotuning_target_cache_memory_usage: 758M
+matrix_synapse_caches_autotuning_min_cache_ttl: 5m
 
 # Controls whether Synapse will federate at all.
 # Disable this to completely isolate your server from the rest of the Matrix network.