Fix Github Actions CI load-test job failing due inability to install Feast Python SDK.

[mrzzy]

What this PR does / why we need it:
Github Actions CI load-test job currently produces the following error:

Collecting feast
  Could not find a version that satisfies the requirement feast (from versions: )
No matching distribution found for feast

As there is no feast python SDK built for Python 2.7

Adds install-python action to load-test job to inst

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[mrzzy]

/test test-end-to-end

[mrzzy]

/test test-end-to-end-batch-dataflow

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mrzzy, woop

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[woop]

/lgtm