Add PROPERTY_SELF_CERTIFIED_NETWORK_CAPABILITIES API

This string allows apps add a network_capabilities.xml resource to the
AndroidManifest.xml.

The network_capabilities.xml file will allow application developers to
request for a network capabilities that they want their application to
be able to use. The available capabilities are defined in
ApplicationNetworkCapabilities.java.

Test: atest FrameworksNetTests CtsHostsideNetworkTests
Bug: 266524688
Change-Id: I99b0698748af3cfafa0ff84df0454584dbad88b1