worker: define worker errors

Define worker errors to give more structured
error messages. The error api is:
id: VALIDATION_ERROR_NUMBER, reason: STRING, details: { issues: [{...}, {...}] }

The api was agreed upon with osbuild so that,
in future, osbuild errors will share the same
structure

internal/worker/clienterrors/errors.go

@@ -0,0 +1,43 @@
+package clienterrors
+
+const (
+	ErrorNoDynamicArgs        ClientErrorCode = 1
+	ErrorInvalidTargetConfig  ClientErrorCode = 2
+	ErrorSharingTarget        ClientErrorCode = 3
+	ErrorInvalidTarget        ClientErrorCode = 4
+	ErrorDepsolveDependency   ClientErrorCode = 5
+	ErrorReadingJobStatus     ClientErrorCode = 6
+	ErrorParsingDynamicArgs   ClientErrorCode = 7
+	ErrorManifestGeneration   ClientErrorCode = 8
+	ErrorManifestDependency   ClientErrorCode = 9
+	ErrorBuildJob             ClientErrorCode = 10
+	ErrorUploadingImage       ClientErrorCode = 11
+	ErrorImportingImage       ClientErrorCode = 12
+	ErrorKojiFailedDependency ClientErrorCode = 13
+	ErrorKojiBuild            ClientErrorCode = 14
+	ErrorKojiInit             ClientErrorCode = 15
+	ErrorKojiFinalize         ClientErrorCode = 16
+	ErrorInvalidConfig        ClientErrorCode = 17
+	ErrorOldResultCompatible  ClientErrorCode = 18
+
+	ErrorDNFDepsolveError ClientErrorCode = 20
+	ErrorDNFMarkingError  ClientErrorCode = 21
+	ErrorDNFOtherError    ClientErrorCode = 22
+	ErrorRPMMDError       ClientErrorCode = 23
+)
+
+type ClientErrorCode int
+
+type Error struct {
+	ID      ClientErrorCode `json:"id"`
+	Reason  string          `json:"reason"`
+	Details interface{}     `json:"details"`
+}
+
+func WorkerClientError(code ClientErrorCode, reason string, details ...interface{}) *Error {
+	return &Error{
+		ID:      code,
+		Reason:  reason,
+		Details: details,
+	}
+}