Allow BGP-LS to handle Performance Metrics as per draft "BGP-LS Advertisement of IGP Traffic Engineering Performance Metric Extensions" https://tools.ietf.org/html/draft-ietf-idr-te-pm-bgp-17
Implementation of its new parser needs to:
- Add new entries in bgp-linkstate.yang
- Add new parser in LinkAttributesParser.java
- Add corresponding tests in LinkstateAttributeParserTest.java