Update feast to run on newest release version 0.31

[jperez999]

This PR updates Merlin to run on latest version of feast by completing the following:

• the multi stage examples to run on the latest version of feast
• optimizes path variables
• updates the merlin-ci container to pip install the latest version of feast
• removed unnecessary imports (faiss and filtercandidate) that resulted from flake-nb checks.
• updated the test_integration script in ci to pip install 0.31 version of feast.

For this PR to work, the following PR must be merged first: NVIDIA-Merlin/systems#344 because it updates the feast operator.

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https://nvidia-merlin.github.io/Merlin/review/pr-975

[karlhigley]

@jperez999 It looks like the tests are failing due to downstream notebook tests, which we definitely should be running but probably should not be part of a required PR check. I think I did that, but it needs further attention, because those tests (while informative) should not block this PR.