Migrate AutoOps docs from Opster

### Description

Some AutoOps docs still live on the [Opster site](https://opster.com/docs/autoops/autoops-overview/), which poses the following risks/problems:

- These pages are outdated and we're not actively monitoring them.
- Most of the information doesn't apply to our current AutoOps offering, eg. [AutoOps installation](https://opster.com/docs/autoops/installation/new-autoops-account-instructions/).
- These pages compete with our current [AutoOps docs](https://www.elastic.co/docs/deploy-manage/monitor/autoops) in search results about AutoOps and it's not immediately clear which docs are the "correct" ones.

### What needs to be done

- Investigate if the information on any of these pages is still relevant.
- Migrate relevant information to our current [AutoOps docs](https://www.elastic.co/docs/deploy-manage/monitor/autoops).
- Sunset these pages on the Opster site/set up redirects as necessary.

### Related tasks

- Enhance current [AutoOps docs](https://www.elastic.co/docs/deploy-manage/monitor/autoops)
- Refresh screenshots (and remove where they are not significantly contributing to the user experience)
- Check consistency with the current UI
- Improve cross-linking and visibility of AutoOps in other docs
- Apply style guide changes