[APM] Fix labels.served_from_cache type (#188836)

fixes [#176425](#176425)
fixes [#176544](#176544)

## Summary

The problem happens intermittently, I've managed to reproduce it a few
times though. I suspect that since the es_archive `8.0.0` does not have
a type definition for the `label.served_from_cache` field, it leaves ES
to determine what's the appropriate type, therefore causing ingestion to
sometimes fail.

The `apm_8.0.0` has a type definition for this field for `transaction`
index
https://github.com/elastic/kibana/blob/main/x-pack/test/apm_api_integration/common/fixtures/es_archiver/apm_8.0.0/mappings.json#L18824,
so I followed the same configuration.

Co-authored-by: Elastic Machine <[email protected]>
(cherry picked from commit 850aa69)

x-pack/test/apm_api_integration/common/fixtures/es_archiver/8.0.0/mappings.json

@@ -22988,6 +22988,9 @@
             "multi-line": {
               "type": "keyword"
             },
+            "served_from_cache": {
+              "type": "keyword"
+            },
             "this-is-a-very-long-tag-name-without-any-spaces": {
               "type": "keyword"
             }