Fix CLI entities command & add feature-views command

[tsotnet]

Signed-off-by: Tsotne Tabidze tsotne@tecton.ai

What this PR does / why we need it: Existing CLI entities command is trying to use feast core. Instead, it should be using new FeastStore abstraction. Also, the CLI didn't have a way of accessing feature views, and I'm adding that as well. Here are the 4 new commands:

feast entities list
feast entities describe <entity-name>
feast feature-views list
feast feature-views describe <feature-view-name>

I also noticed that in bunch of places where we want to throw errors, we use Exception class, which has some disadvantages. For example, when you want to catch this error you have to use except Exception as e, which can catch all different kinds of exceptions. In this PR I started a new errors.py class where I introduces some new exception types, so it's easier to catch them.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

Fix CLI entities command & add feature-views command

[woop]

In this PR I started a new errors.py class where I introduces some new exception types, so it's easier to catch them.

Nice!

[woop]

/lgtm

[feast-ci-bot]

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