cli/command/context: test inspecting context with custom metadata

The CLI does not currently expose options to add custom metadata to
contexts, but contexts support them.

- update test-utilities to allow setting custom metadata
- update the inspect test to verify that custom metadata is included
  when inspecting a context.
- update the import/export tests to verify that custom metadata
  is preserved.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 2e9eff235d)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/context/create.go

@@ -24,6 +24,10 @@ type CreateOptions struct {
 	Description string
 	Docker      map[string]string
 	From        string
+
+	// Additional Metadata to store in the context. This option is not
+	// currently exposed to the user.
+	metaData map[string]any
 }
 
 func longCreateDescription() string {
@@ -94,7 +98,8 @@ func createNewContext(contextStore store.ReaderWriter, o *CreateOptions) error {
 			docker.DockerEndpoint: dockerEP,
 		},
 		Metadata: command.DockerContext{
-			Description: o.Description,
+			Description:      o.Description,
+			AdditionalFields: o.metaData,
 		},
 		Name: o.Name,
 	}