Node LTS support and testing

[xirzec]

Today we have a guideline stating we must support all LTS versions of node.
(It's a little out of date, so I have a PR to fix that. )

We currently run most CI against a wide matrix from 8 to 14:

https://github.com/Azure/azure-sdk-for-js/blob/master/eng/pipelines/templates/jobs/archetype-sdk-client.yml

There are some irregularities we should think about:

1. Node8 has been End of Life since the beginning of 2020, but we still test on it and code against it.
2. cosmos only runs integration tests on Node8: https://github.com/Azure/azure-sdk-for-js/blob/master/eng/pipelines/templates/stages/cosmos-sdk-client.yml

It's unclear at this time when we should drop support for a particular Node version. It's also unclear what our guidance should be for running against smaller matrices. Cosmos' current configuration, for example, won't catch breaking changes in the latest Node version.

/cc @ramya-rao-a @bterlson @southpolesteve for thoughts.

[ghost]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @southpolesteve, @zfoster

[southpolesteve]

I'm not sure why Cosmos only runs against Node 8. No issue from our side running the full matrix.

As much as I would like to drop Node 8 support in v4, our telemetry suggests that may not be wise. Talked with @bterlson this last week. Happy to share more over teams.

[xirzec]

@ramya-rao-a is this issue irrelevant now?

[ramya-rao-a]

Yes, thanks @xirzec

The latest support policy clarifies our support for the different Node.js versions

#15647 removes Node.js 8 from our test matrix
#15787 updates the cosmos test runs to run on Node.js 10 instead of 8

For more on dropping Node.js 8, please see #7022