feat: support const in example generation

[markrzen]

Description

Support const during example generation

Continuation of: #1143

Motivation and Context

This helps produce better example code, which can be copy/pasted without manual modifications.

How Has This Been Tested?

Both tested locally against my schema, and a added unit test.

Screenshots (if appropriate)

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist

• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes if appropriate.
• All new and existing tests passed.

[markrzen]

@sserrata Sorry for the notification. You had reviewed the previous PR #1143, where I missed the need to add const support in example generation.