An ability to change piece spawn height in custom rooms/games

[KonSola5]

Checklist

• I've checked both open and recently closed issues to ensure this feature is not already requested.
• I am using the newest version of TETR.IO.
• I am certain this is a feature request, not a bug.
• I've thought this feature through properly.

Is your feature request related to a problem? Please describe.

TETR.IO always spawns pieces on (height + 1) row (row 22 with default board size), so if you wish to more accurately replicate for example, NES ruleset (spawns pieces mostly on row 19), TE:C (spawns pieces on row 20), or PPT ruleset (spawns pieces on row 21), you can't do that.

Describe the solution you'd like

An option to change the piece spawning offset, relative to the field height (with 0 being right above the skyline).
Default offset would be 1.

This should be also validated so the spawnpoint always lays in bounds (so not below the floor and not above the buffer zone)

Describe alternatives you've considered

Changing field height. However this resizes the board, and Lock Out can't be replicated accurately.

Additional context

No response