Restructure for better rendering on TF Registry

[krowlandson]

Overview/Summary

Updates the README structure for better rendering on the Terraform Registry.

Once merged, the resulting commit on main will be used to rebase release v1.0.0 as no code changes made to the actual Terraform Module.

This PR fixes/adds/changes/removes

1. Reduces maximum list indentation from 3 to 2 levels.
2. Documentation heading removed and ToC reduced to level 1 headings only for improved readability.
3. Links to Wiki examples moved from ToC to Examples section.
4. Added references to using the Provider Configuration in the Overview section.
5. Replaced content of the Contributing section with links to the associated Wiki docs.

Breaking Changes

none

Testing Evidence

Benefit of changes will only be visible on Terraform Registry once included in a release.

As part of this Pull Request I have

• Checked for duplicate Pull Requests
• Associated it with relevant issues, for tracking and closure.
• Ensured my code/branch is up-to-date with the latest changes in the main branch
• Performed testing and provided evidence.
• Updated relevant and associated documentation.
• Updated the "What's New?" wiki page (located in the Enterprise-Scale repo in the directory: /docs/wiki/whats-new.md)

[jtracey93]

LGTM 🚢

[jtracey93]

/azp run unit

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).