Fix Query Planner able to find struct field with capital letters

[dttung2905]

Which issue does this PR close?

• Closes Query Planner Unable to Find Struct Fields with Capital Letters #16648

What changes are included in this PR?

My way of fixing is to follow exact match first which is the current way, then fall back to case-insensitive match if there is no exact match. I'm relatively new to Rust, coming from Golang background so your feedbacks are super valuable for me

I also tested out the test case in the github issue

❯ ./target/debug/datafusion-cli
DataFusion CLI v48.0.0
> select thing.fooBar from 'test.json';
+-------------------------+
| test.json.thing[foobar] |
+-------------------------+
| not going to find me    |
+-------------------------+
1 row(s) fetched. 
Elapsed 0.009 seconds.

> \q
❯ cat test.json
{"thing": {"fooBar": "not going to find me"}}