Docs: Implementation patterns for platform partners

What does this MR do?

Update the AWS Installation documentation:

• move the existing manual install instructions page to a subpage and mark it as DEPRECATED in order to clear the 'install/aws' url to be an index to all AWS documentation
• created a new 'install/aws/index.md'
  • to give an overview of how the AWS opinionated documentation relates to and builds upon the reference architectures
  • to have an index of sub-pages at the bottom.
• provides a new sub page for GitLab Cloud Native Hybrid on AWS EKS - which provides critical Bill Of Materials lists for the upcoming AWS Quick Start for GitLab Cloud Native on EKS.

Screenshots or Screencasts (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

NOTE: Current Review App Mapping

• Compare review app root: http://main-ee-65887.178.62.207.141.nip.io/ee/install/aws/index.html
• To the original: https://docs.gitlab.com/ee/install/aws/