Upgrade code generation to swagger v3 to avoid pulling in deprecated code.

[tkaitchuck]

Problem description
Currently following the instructions in .../controller-api/src/main/swagger/README
Results in a class that does not properly compile:
https://github.com/pravega/pravega/blob/master/controller/src/main/java/io/pravega/controller/server/rest/generated/api/RFC3339DateFormat.java
Which runs into a warning because of: FasterXML/jackson-databind#1786
This was reported swagger-api/swagger-codegen#8705 and OpenAPITools/openapi-generator#1053

Problem location
Dependencies

Suggestions for an improvement
It may be resolved in swagger version 3. https://mvnrepository.com/artifact/io.swagger.core.v3
We should update our code to work with the new version of swagger and re-generate the relevant code.