Using regex matches in redirects

** Please describe which feature you have a question about? **
Rewrites and redirects

** Provide additional details**
I have a SPA that does client side routing. However I've been working on my SEO and want to get good 301s and 404s. I am also pre-rendering my routes to static html files, which to some degree makes the routing not behave as a SPA from a server perspective.

So I want to have:
301 "/something/" -> "/something"
301 "/something/index.html" -> "/something"
200 "/something" -> "/something/index.html"

However I also need to handle some static files that are present in the root directory, like the favicon and robots.txt etc.

I also have a "static" directory with some other assets in it that I want to exclude from the rewrites and behave like normal 200/404s.

So in my config I have:
```
[
{
"source": "/static/<*>",
"target": "/static/<*>",
"status": "200"
},
{
"source": "/",
"target": "/index.html",
"status": "200"
},
{
"source": "/index.html",
"target": "/",
"status": "301"
},
{
"source": "//index.html",
"target": "/",
"status": "301"
},
{
"source": "//",
"target": "/",
"status": "301"
},
{
"source": "",
"target": "<$1>",
"status": "200"
},
{
"source": "/",
"target": "//index.html",
"status": "200"
},
{
"source": "/<*>",
"target": "/404.html",
"status": "404-200"
}
]
```

This ALMOST works, except for the regex rule which is matching the static files in the root. The regex code is correct and is matching to the files I want. However the target location is not correct (results in a 404 response). What I want it to do is much like the rule I have for the "static" directory where it gives an accurate respose for if the file exists or not (200/404). Which means the target of that rule needs to be the regex match.

I have tried using "<*>", "<$1>", and "<1>" with no joy. Can you tell me the correct way to use the match from the regex? Or if not, what would be a better way to configure this?

Start with the AWS Amplify Hosting documentation for rewrites and redirects, then reproduce the posted JSON configuration with a root static file and a file under static. Check how regex captures are supported in source and target fields and whether the desired 200/404 behavior can be verified for existing and missing assets; done means a documented supported configuration or a confirmed limitation and workaround.

Written by the indexing model from the issue text.