[Feature] Add support for Guild Member Flags (#2571)

* implement `GuildUserFlags`

Co-authored-by: Casmir <68127614+csmir@users.noreply.github.com>

src/Discord.Net.Core/Entities/Users/GuildUserFlags.cs

@@ -0,0 +1,42 @@
+namespace Discord;
+
+
+/// <summary>
+///     Represents public flags for a guild member.
+/// </summary>
+public enum GuildUserFlags
+{
+    /// <summary>
+    ///     Member has no flags set.
+    /// </summary>
+    None = 0,
+
+    /// <summary>
+    ///     Member has left and rejoined the guild.
+    /// </summary>
+    /// <remarks>
+    ///     Cannot be modified.
+    /// </remarks>
+    DidRejoin = 1 << 0,
+
+    /// <summary>
+    ///     Member has completed onboarding.
+    /// </summary>
+    /// <remarks>
+    ///     Cannot be modified.
+    /// </remarks>
+    CompletedOnboarding = 1 << 1,
+
+    /// <summary>
+    ///     Member bypasses guild verification requirements.
+    /// </summary>
+    BypassesVerification = 1 << 2,
+
+    /// <summary>
+    ///     Member has started onboarding.
+    /// </summary>
+    /// <remarks>
+    ///     Cannot be modified.
+    /// </remarks>
+    StartedOnboarding = 1 << 3,
+}

src/Discord.Net.Core/Entities/Users/GuildUserProperties.cs

@@ -82,5 +82,13 @@ namespace Discord
         ///     <see langword="null"/> or a time in the past to clear a currently existing timeout.
         /// </remarks>
         public Optional<DateTimeOffset?> TimedOutUntil { get; set; }
+
+        /// <summary>
+        ///     Gets or sets the flags of the guild member.
+        /// </summary>
+        /// <remarks>
+        ///     Not all flags can be modified, these are reserved for Discord.
+        /// </remarks>
+        public Optional<GuildUserFlags> Flags { get; set; }
     }
 }

src/Discord.Net.Core/Entities/Users/IGuildUser.cs

@@ -111,6 +111,11 @@ namespace Discord
         /// </returns>
         DateTimeOffset? TimedOutUntil { get; }
 
+        /// <summary>
+        ///     Gets the public flags for this guild member.
+        /// </summary>
+        GuildUserFlags Flags { get; }
+
         /// <summary>
         ///     Gets the level permissions granted to this user to a given channel.
         /// </summary>