Fetch invalid schemas

[gmcoringa]

With the new version of schema registry (0.8.1) which updates avro to 1.9.1 its not possible to use schemas that are invalid due to validations included in the new avro version.

One case is when you have an invalid schema and you try to fix it, but the schema-registry try to validate the old version, more information -> #617

Another case is using the schema-registry client, for example as the serializer for kafka, because when the client tries to get a schema actually calls addSchemaVersion:

java.lang.RuntimeException: An exception was thrown while processing request with message: [Invalid default for field method: null not a "string"]
        at com.hortonworks.registries.schemaregistry.client.SchemaRegistryClient.handleSchemaIdVersionResponse(SchemaRegistryClient.java:591) ~[schema-registry-client-0.5.4.jar:na]
        at com.hortonworks.registries.schemaregistry.client.SchemaRegistryClient.doAddSchemaVersion(SchemaRegistryClient.java:577) ~[schema-registry-client-0.5.4.jar:na]
        at com.hortonworks.registries.schemaregistry.client.SchemaRegistryClient.lambda$addSchemaVersion$1(SchemaRegistryClient.java:515) ~[schema-registry-client-0.5.4.jar:na]
        at com.google.common.cache.LocalCache$LocalManualCache$1.load(LocalCache.java:4739) ~[guava-jdk5-17.0.jar:na]
        at com.google.common.cache.LocalCache$LoadingValueReference.loadFuture(LocalCache.java:3524) ~[guava-jdk5-17.0.jar:na]
        at com.google.common.cache.LocalCache$Segment.loadSync(LocalCache.java:2317) ~[guava-jdk5-17.0.jar:na]
        at com.google.common.cache.LocalCache$Segment.lockedGetOrLoad(LocalCache.java:2280) ~[guava-jdk5-17.0.jar:na]
        at com.google.common.cache.LocalCache$Segment.get(LocalCache.java:2195) ~[guava-jdk5-17.0.jar:na]
        ... 176 common frames omitted

Note that the stacktrace uses an older version, but the server is updated.

For those who have invalid schemas its not possible to use the new version, unless, all schemas are fixed.

[gcsaba2]

Also mentioned in internal jira CDPD-19155