LogsQL: add switch/case syntax to format pipe for multi-branch conditional formatting

[func25]

Is your feature request related to a problem? Please describe

format already supports if (<filters>), but only as a single condition for the whole pipe. This works for simple cases, but it becomes awkward when one field needs different values for different conditions (if else/ switch case).

In such cases, users currently have to duplicate logic across multiple pipes or build less readable workarounds.

Describe the solution you'd like

Add switch/case support to the format pipe for writing different values into a single destination field based on multiple filter conditions.

Proposed syntax:

| format switch (
  case (status:200) "OK"
  case (status:400) "Error"
  default "Other"
) as status_string

The switch block should evaluate cases from top to bottom and write the first matching result into status_string.