fix(kafka admin): validations and show proper error messages

[rkpattnaik780]

• Check if topic exists before allowing user to prompt values for update.
• Show proper status of Kafka instance while performing topic/consumer group operation.

Closes #712 #726

Verification Steps

1. Try updating a topic that doesn't exist:

./rhoas kafka topic update <non-existent>
> Error: topic "<non-existent>" does not exist in Kafka instance "test-instance"

2. Delete a Kafka instance from UI, try listing all the topics in that Kafka instance.

./rhoas kafka topic list
> Error: Kafka instance "<random name>" is being deleted

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation change
• Other (please specify)

Checklist

• Documentation added for the feature
• CI and all relevant tests are passing
• Code Review completed
• Verified independently by reviewer