[Metricbeat] [Elasticsearch] Error in case of missing settings key

[3kt]

With the addition of an extra settings API call in PR in the Metricbeat Elasticsearch module, there is a possible misbehavior if one of the key isn't found (or its path for that matters).

This results in error like the one below:

5 errors: failure adding index settings: failed to get index settings for index .geoip_databases: key not found
[...]

We will want to do multiple things:

1. Ensure we have test coverage for this, as what should cover this is currently skipped.
2. Modify the code so that a missing path or leaf doesn't yield an error. As this is an "internal" field, the absence of the field shouldn't cascade into a frontend error.

[TristanAdams03]

I am experiencing this bug is there a temporary fix until the next patch it is causing my stack to show up as degrading. Thank you