JobCoordinator may be turned off by configuration

[pyalex]

What this PR does / why we need it:

We need option to deploy core without job management

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

Added the option of turning ingestion job management on or off.

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[woop]

/lgtm

[woop]

/kind feature

[ches]

We pretty much coincidentally implemented the same thing at the same time.

Illuminating a use case for anyone following along: you probably want to deploy redundant Core instances for availability. They will not play well together if they all try to manage jobs, duplicating things and stomping on each other.

A boolean flag serves as poor man's leader election, enable it on only one instance in a deployment. If the active coordinator fails, remediate by bringing it back to life or deploying a new instance with this flag enabled.

Although not specific to the job coordination, a related concern is that Serving instances talk to Core to load and cache registered feature set specifications. The caching provides a layer of resilience if Core instances fail. Enabling a means of load balancing / round-robin for the gRPC connections from Serving to Core instances may be desirable however.

Some of this may have a home in Feast operations guide documentation.