fix: Typos and style guide violations in NGINXaaS azure certificates doc

[linamadigan]

Proposed changes

• fixed typos
• fixed style guide violations (no gerunds in headings, sentence case in
  headings)
• fixed markdownlint (blank lines around tables/multiple blank lines)

Checklist

Before sharing this pull request, I completed the following checklist:

• [ x ] I read the Contributing guidelines
• [ x ] My branch adheres to the Git conventions
• [ x ] My content changes adhere to the F5 Technical Writing Style Guide
• [ x ] If my changes involve potentially sensitive information¹, I have assessed the possible impact
• [ x ] I have waited to ensure my changes pass tests, and addressed any discovered issues

Footnotes

1. Potentially sensitive information includes personally identify information (PII), authentication credentials, and live URLs. Refer to the style guide for guidance about placeholder content. ↩

[JTorreG]

merging with one approval : typo fixes. build is working