Schema registry URL in configuration file not picked-up before SerDe flags validation

[Perdjesk]

Steps to reproduce

1. Create a configuration file:

$ cat kafkacat.conf
schema.registry.url=http://schema-registry-url:8080
metadata.broker.list=mybroker

2. Run a kafkacat consumer using the above configuration file and enable avro SerDe

docker run -it -v "$PWD"/kafkacat.conf:/root/.config/kafkacat.conf --network=host edenhill/kafkacat:1.5.0 -C -t syslog -s avro

Actual result

% ERROR: -r requires -s avro and vice-versa

Expected result

The -r flag configuration must be picked-up from configuration file before flags validation.

[edenhill]

Fixed on master