EntityLink Python Parser

[pmbrull]

We need to build a parser for EntityLink following the work on javascript and Java

https://github.com/open-metadata/OpenMetadata/blob/main/openmetadata-core/src/main/java/org/openmetadata/core/util/MessageParser.java

Instead of building it ad-hoc, let's use ANTLR similar to how it was implemented for the FQN