Introduce edit-sign flag

[SirYwell]

Overview

Fixes #4205

Description

Introduces a flag to allow sign editing separately from the use flag. The use flag is typically used to allow interactions with shops etc, but players should not be able to just edit every sign if the use flag is needed.

Submitter Checklist

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[NotMyFault]

The flag addition should also be documented in https://github.com/IntellectualSites/documentation/tree/main/plotsquared

[Tamikaschu]

Wouldn't it makes sense to add a bypass permission to the flag? Admins who are not added on the plot cannot create signs with text. They all appear empty when placed since the PlayerSignOpenEvent is cancelled.

[Leahcimkrob]

I'm already looking for that too. You can get around this either way if the admins trust each other for a moment. But it doesn't make sense that an admin can't edit or set the signs.