Record exception with stack trace on log records

[ol1s]

Currently, exceptions on spans ARE presenting a useful stack trace whereas exceptions in logs ARE NOT presenting the stack trace.

As per otel semantic conventions:

Exceptions SHOULD be recorded as attributes on the LogRecord passed to the Logger emit operations

https://opentelemetry.io/docs/specs/semconv/exceptions/exceptions-logs/

This proposal records the exception with stack trace on the log record, using a similar implementation to the Span.php

[ol1s]

Opened in the main repo instead of sub tree open-telemetry/opentelemetry-php-contrib#410