Feature: ConVars for `weapon`/`item`/`ammo` respawn time

[SergeyShorokhov]

// The respawn time for items (such as health packs, armor, etc.).
// 0 - disable delay
//
// Default value: "30"
mp_item_respawn_time "30"

// The respawn time for weapons.
// 0 - disable delay
//
// Default value: "20"
mp_weapon_respawn_time "20"

// The respawn time for ammunition.
// 0 - disable delay
//
// Default value: "20"
mp_ammo_respawn_time "20"

• await #982