Add SSL connection parameter for Schema registry

[jlvelez]

Made changes to Kafdrop so that it can connect to a secure Schema Registry endpoint.

Added the following parameters:

• SCHEMAREGISTRY_PROPERTIES : Additional properties to configure the schema registry connection (base-64 encoded). Provides keystore/trustore location and password.
• SCHEMAREGISTRY_TRUSTSTORE : Certificate for schema registry authentication (base-64 encoded). Required for TLS/SSL.
• SCHEMAREGISTRY_KEYSTORE : Private key for mutual TLS authentication (base-64 encoded).

These work similar to

• KAFKA_PROPERTIES
• KAFKA_TRUSTSTORE
• KAFKA_KEYSTORE

[Elpaggio]

Why hasn't this pull request been merged yet?