[ML] Analytics Job: Handle index patterns in the same way as search and reindex

[hendrikmuhs]

Analytics validation succeeds if at least 1 index is expanded:

"source": {
    "index": ["existing", "missing"]
  },

The validator expands index as a whole without checking individual parts like missing and succeeds because "existing" expands to 1 index.

This is different to search and reindex, which would fail for this case.

Additionally patterns like this:

"source": {
    "index": "missing*"
  },

fail, but are valid for reindex/search.

Similar to: #49851

[elasticmachine]

Pinging @elastic/ml-core (:ml)