[google search console] invalid dimensions in custom report should be identified during check instead of discover

[brianjlai]

Current Behavior

When a customer specifies an invalid dimension in their custom report, it will currently fail during the discover with an invalid key in the map as per: https://github.com/airbytehq/airbyte/blob/master/airbyte-integrations/connectors/source-google-search-console/source_google_search_console/streams.py#L329-L342

Expected Behavior

Since the custom report is defined as a config option on the connector, we can verify the validity of their custom report dimensions during the check instead of during discover. This could be done by invoking the self.get_json_schema() for the SearchAnalyticsByCustomDimensions stream as part of the check_connection() method whenever a custom report is defined as a config option.

[grubberr]

I have improved custom_reports.dimension validation in this PR #18568