[translator/loki] loki exporter add raw log export format

[jmichalek132]

Description:

As discussed in slack, right now when using the loki exporter, to access the raw log message we need to run a query like this:

{exporter=OTLP} | json | line_format `{{.body}}`

To avoid having to parse the log messages twice, I propose introducing raw format. Instead of sending the whole log record (including attributes and resources attributes) as a json, just send the body containing the actual log message.

Link to tracking Issue:

Related to #18742

Testing:
Tested in our testing environment with locally built image.

Documentation:

[runforesight]

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[jpkrohling]

@mar4uk, could you please review this one?

[mar4uk]

could you please add tests to cover conversion to the new format?

[jmichalek132]

could you please add tests to cover conversion to the new format?

Added test, is this good enough?

[mar4uk]

LGTM 👍
Some checks have failed. Please run make gofmt all as recommended here

[jmichalek132]

Thank you @mar4uk for the review, is there anything else I need to do to get this merged :) ?

[kovrus]

Can you please document it in loki exporter?

[jmichalek132]

Can you please document it in loki exporter?

Would this be updating the readme for the exporter?
Currently, there is no mention of the different formats there.

[kovrus]

Can you please document it in loki exporter?

Would this be updating the readme for the exporter? Currently, there is no mention of the different formats there.

We probably should document how to configure the format via the loki.format attribute hint.

[mar4uk]

let's add the format section first in the separate PR #19734

When it is merged, let's add information about format=raw here