Add ISAR EXT REND commands to improve coverage

• Related issues: #1112 (closed)
• Requested reviewers: @kiene, @ripinder.singh, @tyagiri

Reason why this change is needed

Complete conformance coverage job with ISAR ext. renderer commands.

Description of the change

The scripts/parse_commands.py script doesn't parse the ISAR EXT REND command. As a result, the ivas-conformance-linux job doesn't trigger some of the ISAR funtions, such as the PLC. The script is modified to include parser for these commands.