[non-forked] 🐛 Source Fauna: fix bug during discover step

[natalyjazzviolin]

What

Non-forked branch of #20275 to check build.

In the fauna source, discover would crash if there were any indexes with no terms or no values. This PR fixes that bug.

How

Bug is fixed, and added a test to validate it.

Recommended reading order

1. x.java
2. y.python

🚨 User Impact 🚨

None.

Pre-merge Checklist

Expand the relevant checklist and delete the others.

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[natalyjazzviolin]

The connector was tested and published , and fixed in the original PR:
#20275 (comment)