hardfork: add a get_ideal_version(uint64_t) function

It returns the ideal version for a given height, which is
based on the minimum height for a fork, disregarding votes

src/cryptonote_core/hardfork.h

@@ -167,6 +167,13 @@ namespace cryptonote
      */
     uint8_t get_ideal_version() const;
 
+    /**
+     * @brief returns the "ideal" version for a given height
+     *
+     * @param height height of the block to check
+     */
+    uint8_t get_ideal_version(uint64_t height) const;
+
     /**
      * @brief returns the current version
      *