Backport #566 & #647 to v0.3

[ches]

What this PR does / why we need it:

The indexes added in #566 are an important fix. They weren't backported for v0.3 yet, so this does that in one combined commit of #566 and its bug fix #647.

The inverse join column name in v0.3 was feature_set_id, not feature_sets_id (which is a bit weird honestly and it was either a breaking change for v0.4 when projects were added, or backporting it to v0.4 was actually a breaking change mid-v0.4, I'm not sure which yet—see the blame walk below).

I've preserved feature_set_id so this is not a breaking change for v0.3.

Walking the blames of feature_sets_id:

• fdd7291
• https://github.com/gojek/feast/pull/393/files#diff-23d202566aa4be59004b3892de68f7d3
• fddafdd

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[APPROVALNOTIFIER] This PR is NOT APPROVED

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[ches]

/assign @zhilingc

[ches]

Guessing the CI build for v0.3 might be a goner at this point 😅

[khorshuheng]

Guessing the CI build for v0.3 might be a goner at this point 😅

Most likely related to this: #657

[ches]

Most likely related to this: #657

Yep, I saw your PR backporting the change to v0.4, I will take a look into doing the same for v0.3 soon since it's still relevant for us.

[ches]

Oh you already did, #657 is the new backport 🎉

[woop]

/retest

[khorshuheng]

/lgtm