Add PAPI placeholder support.

[LlmDl]

Description:

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New Nodes/Commands/ConfigOptions:

%siegewar_siege_battlesession_time_remaining% - How much time is left in the current battle session.
%siegewar_player_is_sieged% - Returns true or false based on whether a player has a siege.
%siegewar_player_immunity_timer% - Returns information about immunity time for the player's town.
%siegewar_player_siege_attackers% - Returns the information about the attackers of a siege, if the player has one.
%siegewar_player_siege_defenders% - Returns the information about the defenders of a siege, if the player has one.
%siegewar_player_siege_progress% - Returns the information about the status of a player's siege, if they player has one.
%siegewar_player_siege_battle_sessions_remaining% - Returns the information about the number of remaining battle sessions if a player has a siege.

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Relevant Issue ticket:

Closes #1005

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• I have tested this pull request for defects on a server.

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