fix: execute template in expandAlias for -a flag

[KIBruh]

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