fix: stop command missing --name flag to specify which instance to stop

[A-d-i-t-y]

Why we need this:
The start command supports --name flag to name a Microcks instance
but the stop command has no --name flag. Users cannot specify which
instance to stop when multiple instances exist.

How this will help:
Adding --name flag to stop command makes it consistent with start
command and allows users to stop a specific named instance.

Problem

microcks start --name myinstance ✅ works
microcks stop --name myinstance ❌ flag does not exist

The stop command always resolves the current context instead of
allowing the user to specify which instance to stop by name.

Fix

• Add --name flag to stop command
• Pass name to ResolveContext() so correct instance is stopped
• Remove unnecessary empty fmt.Println() call