Remove redundant permission checks for Flag List Command

[gamecrash534]

Overview

This PR relates to an issue where a player cannot list all plot flags available if he isn't on a plot where he has permissions to change them.

Description

As said in the overview, this PR aims to solve the issue of a player not being able to use /plot flag list if he does not meet the requirement of standing on a plot where he has permission to change these flags. The idea behind this issue being that a player should be able to view the list of flags regardless of permission to change them - as one might be on a plot of another player and wants to find the correct flag to do XY, e.g. to help him out. This eliminates the need to visit / google the documentation or go to a own plot just to enter this command and view the available flags. It still, though, needs the plots.flag.list-permission to be executed.

Submitter Checklist

• Make sure you are opening from a topic branch (/feature/fix/docs/ branch (right side)) and not your main branch.
• Ensure that the pull request title represents the desired changelog entry.
• New public fields and methods are annotated with @since TODO.
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[SirYwell]

From my understanding, the plots.flag.list permission allows to use the command on all plots, while without the permission, using it isn't even allowed on the own plot, right?
In that case, I think we should rather add another permission (e.g. plots.flag.list.other). Without that permission, checkRequirements should still be called. This way, it is possible to control whether the user can run the command on other plots too.

[gamecrash534]

Currently the permission only allows you to list the flags when you're on a plot where you have permission to change them (e.g. a plot owner). But adding a new permission for this also seems like the best approach, yes. I can also implement this, as it shouldn't be that hard