Expose upsertWithWhere

[Amir-61]

• Expose upsertWithWhere

Backport of #2539

[Amir-61]

@slnode test please

[Amir-61]

• @bajtos @rmg It seems Loopback@2.x does not fetch the latest changes from loopback-datasurce-juggler@2.x; in other words, it does not fetch the changes we have landed by this PR in loopback-datasurce-juggler@2.x; do we need to release a new npm version for loopback-datasurce-juggler@2.x to have the changes in this PR?
• @bajtos @jannyHou When I test this PR using npm link to the latest commit of loopback-datasource-juggler@2.x on my local machine, all tests pass except this relationship test in test/relations.integration.js, which is definitely irrelevant to this PR. Can we merge this PR since the failure is irrelevant to this PR?

[Amir-61]

Oh Please ignore my earlier comment#2722; it seems it started re-running tests now and they are pulling the latest changes from loopback-datsource-juggler@2.x this time; it seems they started passing now.

@bajtos There was some small merge conflicts. PTAL this back-porting PR. I see some failures (downstreams and some dependants), I do not think if they are relevant, am I right?

[bajtos]

LGTM.

[mountain1234585]

@Amir-61 Thanks a lot for getting this in.

[Amir-61]

No Problem. Enjoy it 🎊 It will be available in the next NPM release.

[Amir-61]

Relate to #2729