Add native types for Python SDK online retrieval

[terryyylim]

What this PR does / why we need it:
Allows user to pass in a more readable form of EntityRow, using Python native form, for get_online_features method. Also, users are now able to convert the response in a more readable form by using to_dict().

Which issue(s) this PR fixes:

Fixes #766

Does this PR introduce a user-facing change?:

Users can now use `to_dict()` after getting the response from python SDK's get_online_features to convert response to a more human readable form.

[woop]

Allows user to pass in a more readable form of EntityRow

Does this PR introduce a user-facing change?: NONE

Seems contradictory x_X

[woop]

Please update the Gitbook examples and tutorials as well to this new format.

[terryyylim]

/retest

[terryyylim]

/retest

[terryyylim]

/test test-end-to-end

[terryyylim]

/test test-end-to-end-auth

[terryyylim]

/test test-end-to-end-auth

[terryyylim]

/test test-end-to-end-auth

[terryyylim]

/test test-end-to-end-auth

[woop]

/lgtm

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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