New command "marker" (some kind of teleportation points)

This new command would be used to create some kind of waypoints that can allow players to store coordinates very easily with commands.
These markers are unique to each entity, so when using the command, we need to specify we are targeting the marker of which entity.

"/marker add"
"/marker modify"
"/marker remove"
"/marker copy" copy the marker of an entity to another, if a marker with the same name already exist, it just replaces it.
"/marker teleport" teleport a player to a specific marker of a specific entity.

Here are some examples to make it more clear:

/marker add Player1 marker_test1 2 70 12 (<entity> <marker> <position>)

/marker modify Player1 marker_test1 6 71 -23 (<entity> <marker> <position>)

/marker remove Player1 marker_test1 (<entity> <marker>)

/marker copy Player1 marker_test1 Player2 marker_test1 (<entity> <marker> <target> <target marker>)

/marker teleport Player2 Player1 marker_test1 0 0 0 180 90 (<target> <entity> <marker> <offset> <rotation>)

The command could also be used with the "execute" command, such as:
/execute at marker @s marker_test1 ...

And so the original "at" option of execute command would be "entity", used like that:
/execute at entity @s ...
(Or maybe just add "marker" option instead of replacing "at".)

This feature would be useful for map making or for datapacks to teleport players between specific points or even between dimensions as for now, we don't have any way to really store coordinates to use them later with a command.