Add an (optional) configurable delay to boss summons, via totems, spawn eggs, and world spawns

[Opalinium]

Is your feature request related to a problem? Please describe. Partially. I have received complaints about bosses instantly attacking users as soon as they are summoned, which gives them no chance to get to a safe distance away and allows bosses to get 'cheap hits' on players.

Describe the solution you'd like I would like to request that bosses have a config arg that determines a spawn-delay for their summoning, if applicable