feat: add transactions support

[darknos]

add base transaction support for for mongodb v4+ shard and replica sets

Tests were copied from https://github.com/strongloop/loopback-connector/blob/master/test/transaction.test.js but skip by default, because we need replica set for tests.

I use run-rs for testing

run-rs -v 4.2.0 --host localhost --portStart 27000

just remove .skip from test/transaction.test.js to run it

Checklist

• DCO (Developer Certificate of Origin) signed in all commits
• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• Commit messages are following our guidelines

[dhmlau]

@darknos, thanks for the PR. Could you please add tests as well? Thanks.

[darknos]

@dhmlau added. (I missed the file when comiited last time)

[darknos]

@darknos, thanks for the PR. Could you please add tests as well? Thanks.

any news?

[taicho]

@dhmlau Also looking for news on this...

[marioestradarosa]

Not so sure if there was a chai feature you required that mocha doesn't have it.

[marioestradarosa]

@darknos great Job, many thanks for this PR. I only had two minor comments about the chai-as-promise package. I fetched your PR locally in my machine and all works perfectly without these two references for this package.

Also, please squash your commits to keep the history tidy and easier to digest.

[darknos]

@marioestradarosa Hi, could you help to understand what the problem with PR Builder?

I did all requested changes but don't have access to Jenkins to check the problem

[achrinza]

Hi @darknos, apologies for not noticing your query earlier.

As part of LoopBack 4 joining the OpenJS Foundation, we're in the midst of migrating the CI infrastructure from Jenkins to GitHub Actions and Travis CI.

Let me see if I can sort it out from my end and get back to you.

[achrinza]

Yikes! That wasn't supposed to happen... Really sorry about that 🙇

I've re-pushed the commit under #633 as an interim.

If you have a local copy, feel free to force re-push it to reopen this PR.