PEL: private header in JSON

The PELTool application is able to convert sections to JSON. This commit
takes care of converting the private header section to JSON.

private header section in JSON sample:

"Private Header":[
 {"Section Version": "1"},
 {"Sub-section type": "0"},
 {"Log Committed by": "0x1000"},
 {"Entry Creation": "10/24/2019  15:50:08"},
 {"Entry Commit": "10/24/2019  15:50:08"},
 {"Creator ID": "BMC"},
 {"Creator Implementation": ""},
 {"Platform Log ID": "0x50000004"},
 {"Log Entry ID": "0x50000004"}
]

Signed-off-by: Aatir <aatrapps@gmail.com>
Change-Id: I8b0d7dc7b70cd2a03f67f7c9a48755803634005d
diff --git a/extensions/openpower-pels/private_header.hpp b/extensions/openpower-pels/private_header.hpp
index 1302182..dd0d504 100644
--- a/extensions/openpower-pels/private_header.hpp
+++ b/extensions/openpower-pels/private_header.hpp
@@ -219,6 +219,12 @@
                sizeof(_creatorVersion) + sizeof(_plid) + sizeof(_id);
     }
 
+    /**
+     * @brief Get section in JSON.
+     * @return std::optional<std::string> - Private header section's JSON
+     */
+    std::optional<std::string> getJSON() const override;
+
   private:
     /**
      * @brief Fills in the object from the stream data