[TF2] Restore the ability to voice command spam as an optional feature for server operator

[num-get]

https://youtu.be/uyjZ45GJwPk Before 2018, the community server operators were able to enable voice command spam by using sourcemod with "sm_cvar tf_max_voice_speak_delay -1" command. But during 2018, the malicious actors were able to lag any servers by simply spamming the voicemenu command as fast as possible. Valve fixed this by adding 0.3 seconds delay every time the client calls for the command. But by doing so, it's now impossible to use voice command faster than 0.3 seconds.

In order to restore this feature without getting rid of the rate limiter entirely, I introduce this new convar "tf_voice_command_rate_limit". Community server operators could use the command "sm_cvar tf_voice_command_rate_limit" and set the value as low as 0.05 to restore this feature. The lower bound value for tf_max_voice_speak_delay command is also removed for the same reason.