Update high-availability-network-load-balancer.md

[willfranx]

Proposed changes

Write a clear and concise description that helps reviewers understand the purpose and impact of your changes. Use the
following format: Updated all titles in high-availability-network-load-balancer.md from title case to sentence case

Problem: Updating titles (headings) on this page to use sentence case rather than title case.

Solution: I replaced capital letters in headers with lowercase, doing my best to follow the rest of the documentation and what was capitalized.

Testing: N/A / None, other than to view the page in markdown preview to ensure it looks correct.

If this PR addresses an issue on GitHub, ensure that you link to it here:

Closes #231 : #231

Checklist

Before merging a pull request, run through this checklist and mark each as complete.

• I have read the contributing guidelines
• I have signed the F5 Contributor License Agreement (CLA)
• I have rebased my branch onto main
• I have ensured my PR is targeting the main branch and pulling from my branch from my own fork
• I have ensured that the commit messages adhere to Conventional Commits
• I have ensured that documentation content adheres to the style guide
• If the change involves potentially sensitive changes¹, I have assessed the possible impact
• If applicable, I have added tests that prove my fix is effective or that my feature works
• I have ensured that existing tests pass after adding my changes
• If applicable, I have updated README.md and CHANGELOG.md

Footnotes

1. Potentially sensitive changes include anything involving code, personally identify information (PII), live URLs or significant amounts of new or revised documentation. Please refer to our style guide for guidance about placeholder content. ↩

[github-actions]

✅ All required contributors have signed the F5 CLA for this PR. Thank you!
_{Posted by the CLA Assistant Lite bot.}

[willfranx]

I have hereby read the F5 CLA and agree to its terms

[ADubhlaoich]

LGTM! Thanks for contributing.

[mjang]

Thanks for your contribution!