Initial KV API concept

Core/Option/IOptionKey.cs

@@ -0,0 +1,22 @@
+namespace Kruzya.TelegramBot.Core.Option;
+
+/// <summary>
+/// Explains what 
+/// </summary>
+public interface IOptionKey
+{
+    /// <summary>
+    /// The chat identifier where this key is related.
+    /// </summary>
+    public long ChatId { get; }
+
+    /// <summary>
+    /// The Telegram user identifier. May be NULL if this is a simple option for all chat members.
+    /// </summary>
+    public long? UserId { get; }
+
+    /// <summary>
+    /// The unique option identifier.
+    /// </summary>
+    public string Identifier { get; }
+}