fix: 🐛 make log signature not to support promise or observable

[NachoVazquez]

PR Checklist

Please check if your PR fulfills the following requirements:

• [ x ] The commit message follows our guidelines: CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ x ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

log-* methods from LogDriver interface can return Observable and Promise. This behavior is not desired since the LumberjackService cannot determine how to handle different scenarios.

Issue Number: N/A

What is the new behavior?

Make log-* just to return void.

Does this PR introduce a breaking change?

[ x ] Yes
[ ] No

Any third party logger returning an observable or a promise from its log-* methods will suffer from this change since such behavior is not longer supported.

Fix: subscribe to Observables or handle Promise inside log-* methods

Other information