Accepted RFCs Should Be Moved to RFC Folder

[AMZN-Gene]

Problem
As a developer it's difficult finding graphic's RFCs. Currently, I will have to open the sig-graphics issues page, and search through both is:open and is:closed issues to find RFCs that are in-progress and RFCs that have been accepted. Even as an experienced O3D dev, it's tricky to remember where to find the RFCs.

Proposed Solution
I want a central place inside of sig-graphics to find all of the accepted RFCs.

Acceptance Criteria

1. Once the RFCs is reviewed and accepted, the GHI should be closed and immediately move the RFC markdown (.md) into sig-graphics/rfcs folder.
2. The rfcs/README.md should be a table contents of accepted RFCs. RFCs in the README can be categorized (by date, or some other category of the sig's choosing). See the network README.md as an example: it's sorted by date and broken down by the year it was accepted.
   https://github.com/o3de/sig-network/blob/main/rfcs/README.md
3. Standardize the new process for accepting RFCs for future RFCs