[8.x] feat(slo): Add optional pipeline processor in the SLI ingest pi…

…peline for advanced customer (#193628) (#193751)

# Backport

This will backport the following commits from `main` to `8.x`:
- [feat(slo): Add optional pipeline processor in the SLI ingest pipeline
for advanced customer
(#193628)](#193628)

<!--- Backport version: 9.4.3 -->

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

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Add optional pipeline processor in the SLI ingest pipeline for advanced
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Add optional pipeline processor in the SLI ingest pipeline for advanced
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Add optional pipeline processor in the SLI ingest pipeline for advanced
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BACKPORT-->

Co-authored-by: Kevin Delemme <[email protected]>

x-pack/plugins/observability_solution/slo/server/assets/ingest_templates/slo_pipeline_template.ts

@@ -64,6 +64,13 @@ export const getSLOPipelineTemplate = (slo: SLODefinition) => ({
                 .join(','),
       },
     },
+    {
+      pipeline: {
+        ignore_missing_pipeline: true,
+        ignore_failure: true,
+        name: `slo-${slo.id}@custom`,
+      },
+    },
   ],
   _meta: {
     description: 'Ingest pipeline for SLO rollup data',