Render the error message of failed validation as a string

[brokensound77]

The error message for failed query validation is a json object, which renders improperly, making the type hinting useless. We should render it as a string prior to passing it (json.dumps) to be readable in failed unit tests

ex: link

E Error in both stack and integrations checks: {'stack': KqlParseError('Error at line:2,column:5\nUnknown field\n(event.dataset:network_traffic.http or (event.category:network_traffic and network.protocol:http)) and\n http.response.status_phrase:ok and destination.port:9200 and network.direction:inbound and\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^\n\nTry adding event.module or event.dataset to specify beats module\n\nstack: 8.12.0, beats: 8.10.3, ecs: 8.10.0'), 'integrations': KqlParseError('Error at line:3,column:9\nUnknown field\n(event.dataset:network_traffic.http or (event.category:network_traffic and network.protocol:http)) and\n http.response.status_phrase:ok and destination.port:9200 and network.direction:inbound and\n not http.response.headers.content-type:"image/x-icon" and\n ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n\n\tTry adding event.module or event.dataset to specify integration module\n\tWill check against integrations [\'network_traffic\'] combined.\n\tpackage=\'network_traffic\', integration=\'http\', package_version=\'1.25.1\', stack_version=\'8.10.0\', ecs_version=\'8.10.0\'')}

[botelastic[bot]]

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