Add support for optional and repeated fields in generated code

[desaikd]

Currently generator stores all the fields as required but based on ISL these fields could be optional as well as can be repeated.

Optional/Required Fields:

• [ ] Rust
• [X] Java

Occurs with range or more than 1 occurrence value:

• [ ] Rust
• [X] Java

[desaikd]

Optional fields are supported as wrapper primitive classes in Java. Support for optional fields is still pending in Rust.