[FEATURE] PPL Add time modifiers to the multisearch command

Is your feature request related to a problem?
N/A

What solution would you like?
I would like to use the time modifiers of the search command (earliest, latest) in the multisearch command as a more concise way to specify the time ranges for all subsearches.

e.g.

| multisearch earliest=-1d
    [search source=source1 | where field1='value1']
    [search source=source2 | where field2='value2']
| stats avg(field3)

could be equivalent to

| multisearch 
    [search earliest=-1d source=source1 | where field1='value1']
    [search earliest=-1d source=source2 | where field2='value2']
| stats avg(field3)

What alternatives have you considered?

• using earliest and latest on all subsearches
• filtering the multisearch with where and date operations

Do you have any additional context?
N/A

Start by tracing how the PPL multisearch and search commands parse and apply the earliest and latest modifiers. Compare the requested example with the current subsearch behavior, then verify that modifiers on multisearch apply consistently to every subsearch and that existing time-range behavior remains unchanged.