Refactor OTLPMetricsClient to use aggregations

[martialblog]

This would allow for the maxdatapoints pattern we use in other Perfdata Backends.

TODO:

• I think there is still a bug when there are periods of no data

[martialblog]

Also fails when there's too much data:

Error while fetching data: {"root_cause":[],"type":"search_phase_execution_exception","reason":"","phase":"fetch","grouped":true,"failed_shards":[],"caused_by":{"type":"too_many_buckets_exception","reason":"Trying to create too many buckets. Must be less than or equal to: [65536] but this number of buckets was exceeded. This limit can be set by changing the [search.max_buckets] cluster level setting.","max_buckets":65536}} No data received.

[martialblog]

Tried to improve the query: https://github.com/NETWAYS/icingaweb2-module-perfdatagraphs-elasticsearch/tree/experiment-aggs

The PerfdataReponse isn't correct yet, but so far no " too many buckets" error.