[mdatagen] Add log type definition

[sincejune]

Description

This PR added type definition needed for supporting structured logs in mdatagen.

Note:

1. mdatagen api users need to at least add logs: {} to metadata.yaml to enable basic log support
2. the NewLogsBuilder function signature is generated dynamically according to logs config:

   func NewLogsBuilder({{ if .Logs }}lbc LogsBuilderConfig, {{ end }}settings {{ .Status.Class }}.Settings) *LogsBuilder {}
   

Link to tracking issue

Part of #12571

Testing

Added

Documentation

Added

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.41%. Comparing base (cf18559) to head (59c7c79).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12822      +/-   ##
==========================================
- Coverage   91.43%   91.41%   -0.02%     
==========================================
  Files         488      488              
  Lines       26879    26892      +13     
==========================================
+ Hits        24577    24584       +7     
- Misses       1818     1824       +6     
  Partials      484      484              

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[dmitryax]

I don't understand why do we need to add this if it's not being used? What's the plan?

Also I'm still not convinced if we really need to provide framework for structured logs. How do you want to use it? Is there an existing use case in contrib?

Also why not events in that case? OTel events are supposed to be used as structured logs. See https://github.com/open-telemetry/opentelemetry-specification/blob/8bbac83c0c994c0a750cc688935fc1cae7fd39b3/oteps/0202-events-and-logs-api.md and other recent developments around that

[sincejune]

Also I'm still not convinced if we really need to provide framework for structured logs. How do you want to use it? Is there an existing use case in contrib?

We have a similar use case like this and personally I think this is a common use case for scraper based receivers as well.

Also why not events in that case? OTel events are supposed to be used as structured logs. See https://github.com/open-telemetry/opentelemetry-specification/blob/8bbac83c0c994c0a750cc688935fc1cae7fd39b3/oteps/0202-events-and-logs-api.md and other recent developments around that

Looks like events might be more appropriate for this use case. I'm not familiar with events and am I correct in thinking that logs and events are essentially similar, aside from some required fields? I'm open to implementing this with events instead of logs. @dmitryax What do you think?

[dmitryax]

I'm not familiar with events and am I correct in thinking that logs and events are essentially similar, aside from some required fields?

Yes, that should be correct. The event must always have a name field which would be a key in the metadata.yaml similar to a metric name.

I'm open to implementing this with events instead of logs. @dmitryax What do you think?

Yes, let's do it. I'd call this group in metadata.yaml events instead of logs