avoid 500 errors for erroring mutation payloads

[camallen]

zoo-stats-api-graphql/app/graphql/mutations/create_event_mutation.rb

Line 55 in fc45c16

{ errors: [] }

Linked to #120 - convert the mutation error handling to add useful messaging to the response object (idiomatic graphql) and add custom error reporting events in the mutation code.

This would also require a modification to the lambda processing code to reflect on the response object errors key combined with HTTP error codes to determine processing failures.

[camallen]

see details in the comment

zoo-stats-api-graphql/app/graphql/mutations/create_event_mutation.rb

Lines 40 to 54 in fc45c16

	# Note: any import errors above will raise now
	# (500 response) for the incoming mutation request
	#
	# Using 500 response status is not idomatic graphql
	# but it is the easiest way to handle the lamdba function error processing
	# as it stands, https://github.com/zooniverse/zoo-stats-api-graphql/blob/965ac156ad38281458fe347fdf9be5a21249db6d/kinesis-to-http/zoo-stats-api-graphql.py#L20
	#
	# Noting that graphql end points will return 200 even for errored states
	# https://graphql-ruby.org/mutations/mutation_errors
	# https://github.com/rmosolgo/graphql-ruby/blob/master/guides/errors/execution_errors.md
	#
	# the following error payloads ast it stands is useless now
	# but is a placeholder to convert to errors as data in futur
	# and modification of the lambda function result handler
	# to check the response payloads for error states