Handle NaNs in Cloud Foundry metrics

[jsoriano]

There have been reports of Metricbeats using the cloudfoundry module only, that log errors like these ones:

ERROR   [publisher_pipeline_output]     pipeline/output.go:180  failed to publish events: unsupported float value: NaN

ERROR   [logstash]      logstash/async.go:280   Failed to publish events caused by: unsupported float value: NaN

DEBUG   [logstash]      logstash/enc.go:37      Failed to encode event: &{2020-11-16 15:50:08.877478995 +0100 CET {} Not valid json: json: error calling MarshalJSON for type common.Float: invalid character 'N' looking for beginning of value <nil> true}

That seem to indicate that there is a problem like #10849, but in the cloudfoundry module.

As we did with Prometheus in #12084, we may also need to add some defensive code around float values received from the Firehose.

Floats can be received from the Firehose in envelopes of type value (Value field) and in container metrics (CpuPercentage), objects in the firehose are encoded using protobuf, that supports NaN values.

For confirmed bugs, please report:

• Version: 7.7.1, 7.10.0
• Steps to Reproduce: Use the cloudfoundry module (not clear with what metrics).

[elasticmachine]

Pinging @elastic/integrations-platforms (Team:Platforms)