Audit action field optionality

[houqp]

Environment

Delta-rs version: all

Binding: rust

---

Bug

What happened:

Some of the fields are incorrectly marked as optional in action.rs

What you expected to happen:

Make sure optionality annotation matches with what's in delta spec and reference implementation: https://github.com/delta-io/delta/blob/master/core/src/main/scala/org/apache/spark/sql/delta/actions/actions.scala

How to reproduce it:

More details:

Follow up from #370

[mosyp]

We also has to double check changes and do not copy paste 1-to-1 as this example https://github.com/delta-io/delta-rs/pull/417/files/b33124ce41bf4ce9b210fc67a79c8e8590dc72b4#diff-9fb70b66d3f77e15e99399b95228d124db4bd0d898e1e159bf106ccced488332 shows that we could face some issues