Performances improvements

[OniriCorpe]

Problem

• on my server, synapse is slow

Solution

• according to https://matrix-org.github.io/synapse/latest/usage/administration/admin_faq.html#help-synapse-is-slow-and-eats-all-my-ramcpu
  • i added libjemalloc to my matrix-synapse env file
  • i increased SYNAPSE_CACHE_FACTOR to 2

after that my server is much more usable so i modified the package to implement the libjemalloc thing also implemented presence tracking deactivation, since the docs says that it can be the culprit

PR Status

• [x] Code finished and ready to be reviewed/tested
• [x] The fix/enhancement were manually tested (if applicable)