feat: update to observability maturity series docs

[ricegi]

This updates the observability maturity series section with the newly redefined maturity model and introduces value drivers and maturity score cards.

All content is encapsulated in the maturity section.

[CLAassistant]

All committers have signed the CLA.

[github-actions]

Hi @ricegi 👋

Thanks for your pull request! Your PR is in a queue, and a writer will take a look soon. We generally publish small edits within one business day, and larger edits within three days.

Please ensure the propsed changes look good by building it first in your local environment. Refer to this contribution guide to get the site up and running in your local.

If you really require a preview url, reach out to one of the writers and they will generate one for you.