The expandAlias function was parsing the template but never executing it,
resulting in empty output when using the -a (alias) flag with template syntax.
Now properly executes the template with the label map and handles execution
errors by falling back to the original alias string.

Fixes alias templates like:
- check_prometheus m q -a 'Host: {{.hostname}}'
- check_prometheus m q -a 'Status: {{if eq .xvalue "1"}}UP{{else}}DOWN{{end}}'

Includes comprehensive unit tests covering:
- Simple label substitution
- Multiple labels
- xvalue special variable
- Conditional logic (if/else)
- Invalid template fallback