Refactor enum usage in command functions

[Nord1cWarr1or]

This PR refactors enum usage in command functions to address issue #340.

Changes made:

• Removed named enum types (amx_gag_s, args_s) from ConCmd_amx_gag and SrvCmd_AddReason functions
• Added constants (AMX_GAG_ARG_COUNT, ARGS_COUNT) for array sizes and argument counts
• Updated enum to be unnamed in all command functions (matching SrvCmd_AddWhitelistCmd style)
• Replaced sizeof(args) with constant value in SrvCmd_AddReason
• Maintained all functionality while making enum usage consistent across functions

Fixes: #340