[9.0] [Custom threshold rule] Allow group for ip type fields !! (#216062) (#218338)

# Backport

This will backport the following commits from `main` to `9.0`:
- [[Custom threshold rule] Allow group for ip type fields !!
(#216062)](#216062)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

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Co-authored-by: Shahzad <[email protected]>

Author: kibanamachine

x-pack/solutions/observability/plugins/observability/public/components/custom_threshold/components/group_by.tsx

@@ -52,7 +52,7 @@ export function GroupBy({ options, onChange, fields, ...rest }: Props) {
       singleSelection={false}
       selectedOptions={selectedOptions}
       options={fields
-        .filter((f) => f.aggregatable && f.type === 'string')
+        .filter((f) => f.aggregatable && (f.type === 'string' || f.type === 'ip'))
         .map((f) => ({ label: f.name }))}
       onChange={handleChange}
       isClearable={true}