Added default and required fields to Connector configurations

You can now specify required environment variables and their default values for standard configurations and required environment variables for secure configurations in connect.yaml. By defining environment variables as required, you ensure that those deploying your Connector know what values are required. Including a default value for standard configurations also ensures there is a fallback value.

Changes:

• [API] Added required to StandardConfigurationKey on ConnectorStaged.
• [API] Added default to StandardConfigurationKey on ConnectorStaged.
• [API] Added required to SecuredConfigurationKey on ConnectorStaged.