make the adding of all messages to the cache optional

[twonirwana]

This allows it to disable the adding of all messages to the cache and thereby reducing the resources.

[felldo]

Isn't this the effectively the same as DiscordApi#setMessageCacheSize(0,0) ? Even if they are cached for 1 minute as the Javadoc states, I think that isn't that bad?

[twonirwana]

My bot is not that popular (on around 300 servers) and even with setMessageCacheSize(0,0) but i have up to 1000 messages in the cache and get Heap memory was too low to hold all configured messages in the cache. messages (even with 5gig of heap). I did not look at the threads but i think all the cleanup schedules will also be quite active.

[felldo]

There seems to be an issue with this message see #647 so this message is not 100% reliable as far as I have witnessed. Imo the best would be that the issue gets fixed instead of adding a workaround as this seems
to be when looking at the linked issue.

[twonirwana]

Heap memory was too low to hold all configured messages in the cache. was only the reason i looked into the caching. I think adding hundreds of messages to a cache only to remove all of them 60s later is not a optimal usage of resources. If you are interested i could also create a pull request where i replace your self written caching with a Guava Cache, that should be more reliable.