Fix a bunch more typos in model documentation files

[endolith]

Describe the changes you have made:

Fix typos in hosted model documentation files

Remove extra newlines in hosted models documentation files

Correct environment variable syntax in GPT-4 setup documentation

Update hosted models documentation to correct model naming conventions
for Anyscale, AWS SageMaker, and VLLM.

(This is AI-assisted but the changes all look correct to me.)

Reference any relevant issues (e.g. "Fixes #000"):

Pre-Submission Checklist (optional but appreciated):

• I have included relevant documentation updates (stored in /docs)
• I have read docs/CONTRIBUTING.md
• I have read docs/ROADMAP.md

OS Tests (optional but appreciated):

• Tested on Windows
• Tested on MacOS
• Tested on Linux