[receiver/splunk_hec] HEC receiver maps attributes to log record instead of resource

[atoulme]

Describe the bug
In https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/receiver/splunkhecreceiver/splunk_to_logdata.go#L65 we map HEC event fields to log record attributes.
This should instead map to the resource associated with the log records.
If several events have different fields, we will need to create additional resources to match this.

This is in relation to #12747.

Steps to reproduce
Send data to the HEC receiver and output it to file.

What did you expect to see?
Resource attributes correctly filled.

What did you see instead?
Logs have attributes, but not the resource.

What version did you use?
Version: 0.59

What config did you use?
N/A

Environment
N/A

Additional context
None

[github-actions]

Pinging code owners: @atoulme @keitwb. See Adding Labels via Comments if you do not have permissions to add labels yourself.

[github-actions]

This issue has been inactive for 60 days. It will be closed in 60 days if there is no activity. To ping code owners by adding a component label, see Adding Labels via Comments, or if you are unsure of which component this issue relates to, please ping @open-telemetry/collector-contrib-triagers. If this issue is still relevant, please ping the code owners or leave a comment explaining why it is still relevant. Otherwise, please close it.

Pinging code owners:

• receiver/splunkhec: @atoulme @keitwb

See Adding Labels via Comments if you do not have permissions to add labels yourself.

[atoulme]

Thank you for the contribution! Closing.