Fix AlternativeCommandsHandler not detecting some aliases

[JRoy]

Before this PR, AlternativeCommandsHandler would iterate through all the values of the command map rather than going by the keys. This should work with 99.99999% of plugins but for some god forsaken reason Towny (go figures) hides its aliases from Bukkit for the /town command, exclusively. This causes Essentials to not be able to detect the /t alias and therefore not be able to forward it. The new solution was to iterate over all keys in the known commands map which contains all aliases at time of registration and maps them to a Command object. This, for some reason, recognizes the /t alias for Towny's /town command and all is right in the world.

Also included in this PR;

• Bumped Paper Version to 1.16.4
  • Should probably be done during MC updates since it throws peer-not-authenticated errors from time to time otherwise
• Enabled advanced gradle caching
  • Will store caches of the build in gradle cache directory allowing for caches to survive a clean.
• Enabled checkstyle checks before commit in IntellJ
• Added a debug message to indicate Essentials is searching for an alternative command to execute

[ChrisTaylor201]

This also seems to fix aliases of other plugins, for example /msg from ChatManager.

Before

[11:55:45] [Server thread/INFO]: CONSOLE issued server command: /ess ver
[11:55:45] [Server thread/INFO]: Server version: 1.16.4-R0.1-SNAPSHOT git-Paper-352 (MC: 1.16.4)
[11:55:45] [Server thread/INFO]: EssentialsX version: 2.19.0-dev+29-318df64
[11:55:45] [Server thread/INFO]: LuckPerms version: 5.2.67
[11:55:45] [Server thread/INFO]: Vault version: 1.7.3-b131
[11:55:53] [Server thread/INFO]: ChrisTaylor issued server command: /msg
[11:55:53] [Server thread/INFO]: [Essentials] ChrisTaylor was denied access to command.
[11:55:54] [luckperms-scheduler-worker-0/INFO]: [LP] VB > christaylor - chatmanager.bypass.mutechat - false
[11:55:54] [luckperms-scheduler-worker-0/INFO]: [LP] VB > christaylor - chatmanager.bypass.commandspy - false
[11:55:54] [luckperms-scheduler-worker-0/INFO]: [LP] VB > christaylor - essentials.mail - undefined
[11:55:54] [luckperms-scheduler-worker-0/INFO]: [LP] VB > christaylor - essentials.msg - undefined

After

[12:05:27] [Server thread/INFO]: CONSOLE issued server command: /ess ver
[12:05:27] [Server thread/INFO]: Server version: 1.16.4-R0.1-SNAPSHOT git-Paper-352 (MC: 1.16.4)
[12:05:27] [Server thread/INFO]: EssentialsX version: 2.19.0-dev+329-c0321a4
[12:05:27] [Server thread/INFO]: LuckPerms version: 5.2.67
[12:05:27] [Server thread/INFO]: Vault version: 1.7.3-b131
[12:05:34] [Server thread/INFO]: ChrisTaylor issued server command: /msg
[12:05:34] [luckperms-scheduler-worker-0/INFO]: [LP] VB > christaylor - chatmanager.bypass.mutechat - false
[12:05:34] [luckperms-scheduler-worker-0/INFO]: [LP] VB > christaylor - chatmanager.bypass.commandspy - false
[12:05:34] [luckperms-scheduler-worker-0/INFO]: [LP] VB > christaylor - chatmanager.message - true