Add notice field for TYPO3 Security Team

The security team should be able to add a notice to extensions which is shown on the detail page of an extension. The intention of this notice is to show users a warning/recommendation about the given extension e.g. like in https://typo3.org/security/advisory/typo3-ext-sa-2020-002

In general the TYPO3 Security Team recommends to not use development dependencies on production websites.