feat: add scopes to v3 datasets

[minottic]

Description

Reuse findOneComplete and findOneAll for v3 endpoints to enable scopes.

Motivation

Reintroduce loopback3 features to v3 endpoints (removing the support is non backward compatible change), by few findAllComplet branching

Changes:

• findAll, findById and findOne in v3 all use the same function now. Avoids dup, shared with v4, same expected behaviour for the user
• richer swagger for v3 endpoints
• v3 findById supports filtering now
• types extended to union v3 and v4

Tests included

• Included for each change/fix?
• Passing?

Documentation

• swagger documentation updated (required for API changes)
• official documentation updated

official documentation info

[minottic]

depends on #2236 and it's opened against that branch. Will rebase after merge

[nitrosx]

IMHO, using hardcoded "v3" and "v4" values in the functions calls will make the code less transparent, hard to manage and harder to separate by versions later on.
I would like to propose the creation of separated datasets.service.ts for v3 and v4.

[minottic]

fine for me, so these services will then do the branching in your proposal?

[nitrosx]

@minottic if I understand your question correctly, I would create a service v3 which will be used by the all the endpoints of dataset api v3 and a service v4 which will be used by all the dataset endpoints v4.
It will introduce some code duplication for now, but it will make the code easier to read and it will be easier to remove obsolete V3 in the future

[minottic]

ok, I will make a new commit for that