feat: Add new documentation facet to all OL events

[kacpermuda]

ContentType was added to OL documentation job facet in #3748. OL client requirement was bumped in #52075 to include that change.
Now I'm adding a documentation facet to all OL events, with this new content type field.

We're checking all the fields mentioned in this doc: doc, doc_md etc.

This also introduce hierarchy, as we can only include one doc in the facet.
The order for task is the following:

1. doc
2. doc_md
3. doc_json
4. doc_yaml
5. doc_rst

For DAG it's:

1. doc_md
2. description

Also for tasks if task doc is not present, we're including DAG docs (if present).

Most of the lines is from testing it properly in system tests.

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[potiuk]

Rebasing to check compatibility after fixing it in main.

[mobuchowski]

@kacpermuda just one question - is there any practical limit on the size of the documentation? Only thing I'm worried about here is the potential impact on event size.

[kacpermuda]

Yeah, good point, I don't think there is one. We can set some limit in the provider, I'll add some variable for that, wdyt should be the max size of such docs?

I'm not sure if we should allow users to configure this limit, maybe instead we'll introduce some event size limits that can be configured (globally or per transport), if such need occurs.

[mobuchowski]

For now, maybe hardcode the length to something like 64kb and truncate the field if it gets larger?

[kacpermuda]

Added _truncate_string_to_byte_size function and applied it to doc included in OL event. Thanks for the input

[mobuchowski]

Thanks!