Chart: fix securityContext.containers/ingress.apiServer in values.schema.json

[Aakcht]

Fix 2 minor issues in values.schema.json:

• Global securityContexts.containers parameter is not defined in values.schema.json, instead securityContexts.container is present. However in values securityContexts.containers is used: https://github.com/apache/airflow/blob/main/chart/values.yaml#L58
• ingress.apiServer parameter is missing from values.schema.json

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[jscheffl]

Cool!