[TF2] Whitelist these cvars for VScript

[Brain-dawg]

tf_mvm_defenders_team_size
mp_restartround
tf_dev_health_on_damage_recover_percentage
tf_dev_marked_for_death_lifetime
tf_whip_speed_increase

The last 3 are Hidden Cvars.

in order:

1. Allows setting MvM team size to something other than 6
2. Similar to mp_restartgame but interacts with the round timer differently, also displays text on everyone's screen similar to HUD_PRINTCENTER
3. Modifies healing received from Concheror effect (may also affect milk? not sure)
4. Modifies the duration of the "Marked for Death" effect from the Fan O War
5. Modifies the speed boost multiplier for the Concheror and Disciplinary Action speed boost effect