docs(postgres): document AWS IAM authentication for postgresql components

[sicoyle]

Thank you for helping make the Dapr documentation better!

Please follow this checklist before submitting:

• [X] Commits are signed with Developer Certificate of Origin (DCO - learn more)
• [X] Read the contribution guide
• [ ] Commands include options for Linux, MacOS, and Windows within codetabs
• [ ] New file and folder names are globally unique
• [ ] Page references use shortcodes instead of markdown or URL links
• [ ] Images use HTML style and have alternative text
• [ ] Places where multiple code/command options are given have codetabs

In addition, please fill out the following to help reviewers understand this pull request:

Description

For code in this PR that I'm hoping will be merged soon: https://github.com/dapr/components-contrib/pull/3324 Let's hold on this PR until the above gets merged please.

Issue reference

https://github.com/dapr/components-contrib/issues/3254

[github-actions[bot]]

Stale PR, paging all reviewers

[sicoyle]

not stale. This has now been merged in components contrib. This docs PR is g2g for review