Add a bit of QoL related to the Tank

[woisalreadytaken]

• Adds sm_szf_tank_debris_lifetime, which makes debris thrown by Tanks despawn after the specified amount of time. Default is 20.0 and can be set to 0.0 to never despawn. This is to prevent servers from lagging because of too many physics objects being active at once.
• Adds a spawn message for the Tank, similar to other special Infected. Since the Tank now has a "special ability," it makes sense to let players know about it.

[FortyTwoFortyTwo]

Was thinking of just freezing the velocity and remove the collision once it stopped rolling around, as it still can push users like crazy when debris was barely moving.

Can still have the despawn convar.

[woisalreadytaken]

Was thinking of just freezing the velocity and remove the collision once it stopped rolling around, as it still can push users like crazy when debris was barely moving.

done, also added fade out when despawning