Fixes #575

This commit Add support for cap_add & cap_drop which maps to
Pod.Spec.Container.SecurityContext.Capabilities.Add/Drop
Added unit tests for ConfigCapabilities function
Updated conversion.md on support for these keys

pkg/loader/compose/compose.go

@@ -51,8 +51,6 @@ func checkUnsupportedKey(composeProject *project.Project) []string {
 	// to make sure that unsupported key is not going to be reported twice
 	// by keeping record if already saw this key in another service
 	var unsupportedKey = map[string]bool{
-		"CapAdd":        false,
-		"CapDrop":       false,
 		"CgroupParent":  false,
 		"CPUSet":        false,
 		"CPUShares":     false,