JSON logging format

[apolukhin]

At the moment 'tskv' and 'ltsv' logging formats are supported

userver/core/include/userver/logging/format.hpp

Line 13 in f04f773

enum class Format { kTskv, kLtsv, kRaw };

JSON format is a popualr logging format, it should be supported too.

[TertiumOrganum1]

voting for json, but also it would be nice to have a simple format for local output, ideally - to select fields for output. for example, timestamp and msg only

[TertiumOrganum1]

It would be nice to have out if the box 'otlp json' format option for logger 'opentracing' (should be also renamed to 'opentelemetry' or 'otel', as opentracing standard is archived since 2022). Protobuf schema described here: https://github.com/open-telemetry/opentelemetry-proto/blob/v1.3.0/opentelemetry/proto/trace/v1/trace.proto
Json mapping looks like: https://www.honeycomb.io/blog/test-span-opentelemetry-collector

[apolukhin]

Thanks to all the contributors, we now have an understanding of how such logging should look like. Will adopt the functionality and features soon