Add support for external logging schemas

[uniqueg]

Problem

It is currently not possible to describe the shape of logging information. This makes it difficult for clients to make use of structured logging information, if available. For example, if a WES implementation returns logging information in the shape of the OPM provenance model and/or according to the one of the profiles of the Workflow Run RO-Crate collection, even clients capable of interpreting this additional information would need to first guess the shape of the returned information. Moreover, documentation on where to log what is terse in WES, which might lead different implementations to include structured logging information in different places.

Proposed solution

Refine WES's logging capabilities such that there is exactly one place where structured logging information for a given logging level (workflow, task) shall be provided, if available, as well as a means of defining the shape of a given (sub)log in a way that a client can understand. Clearly document the expected usage.

Alternative solutions

NA

Additional context

See metaissue on logging improvements.

[uniqueg]

Almost a duplicate of #13 (but the proposed solution is different)