feat: As a user, I want to make regex-uri able to use nginx context variables for Plugin [proxy-rewrite]

[V1endr3]

Description

Make regex-uri of proxy-rewrite able to use nginx context variables.

Currently, APISIX's plugin proxy-rewrite can rewrite URIs through one of uri and regex_uri.
While using uri, I can pass in a nginx context variable like ${http_SOME_HEADER} to make a header fill into the URI.
While using regex_uri, the only thing I can do is pass in the result of a regex match like $1,$2,etc.
regex_uri feature does not support using nginx context variables to fill a URI.

We have to give up using the nginx context variable if we need to use the regex pattern.

We could consider making it possible by modifying the order of regex match to make it possible to use both of them.
Firstly, fill in nginx context variables and make variables like $1,$2 remain there.
Secondly, match the result of the former step with a regex pattern.

Examples

I have a header like "X-Test-Path: demo", and wanna make it into path while parsing it.

Origin:

• uri: /test/tpath/var?a=1
• headers:
  • X-Test-Path = demo

Expect:

• uri: /test/demo/var
• headers:
  • X-Trans-Path = tpath

I'd like to contribute to this issue!

[shreemaan-abhishek]

I do not agree with this use case going forward. The regex_uri feature is only for uri, it's better to use the serverless plugin for such a niche/customized use case.