Patches to Introduction and Setup

@tpenn updated some of the instructions in Chapter 1: Introduction and Setup to improve clarity and provide additional context for Mac users.

Chapter 20: APIs and REST

Chapter 20 content merged into main branch

Chapter 18: Relationship Mapping and ORM

Migrated Chapter 18 to Hugo and updated to Java 17.

Next Steps for Enums Chapter

Added next steps for the enums chapter.

Chapter 17: Intro to ORM

Chapter 17 content has been merged into the main branch.

Chapter 15: Model Validation

Migrated Chapter 15 content from Sphinx to Hugo and updated to Java 17.

Chapter 19: Authentication

Chapter 19 content merged into main branch.

Chapter 16: Enums merged

Chapter 16 content merged into main branch.

Patch to inheritance chapter

Spacing and directory structure within reading updated

Assignment Formatting Sync

Assignments 1-4 all had tasks. This release syncs the formatting for those tasks ie:

Task 1
Task 2
Task 3