Replace PBKDF2-SHA1 with PBKDF2-SHA512

This also migrates already created passwords on login

Source for the number of iterations:
https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html#pbkdf2

MediaBrowser.Model/Cryptography/Constants.cs

@@ -0,0 +1,23 @@
+namespace MediaBrowser.Model.Cryptography
+{
+    /// <summary>
+    /// Class containing global constants for Jellyfin Cryptography.
+    /// </summary>
+    public static class Constants
+    {
+        /// <summary>
+        /// The default length for new salts.
+        /// </summary>
+        public const int DefaultSaltLength = 128 / 8;
+
+        /// <summary>
+        /// The default output length.
+        /// </summary>
+        public const int DefaultOutputLength = 512 / 8;
+
+        /// <summary>
+        /// The default amount of iterations for hashing passwords.
+        /// </summary>
+        public const int DefaultIterations = 120000;
+    }
+}