The `regex_uri` of `proxy-rewrite` plugin is definition limits the length to 2, but the document supports multiples of 2。

[hanrea]

Issue description

https://github.com/apache/apisix/blob/4f5ac5870976a26983b9d511c635c51652c6f70f/apisix/plugins/proxy-rewrite.lua#L197

https://github.com/apache/apisix-dashboard/blob/e0290c81cb3972978f0d1e3066db4d17dc6c14d1/api/conf/schema.json#L8267

Expected behavior

supports multiples of 2.

How to Reproduce

no

Screenshots

No response

Environment

• apisix version (cmd: apisix version):
• OS (cmd: uname -a):
• OpenResty / Nginx version (cmd: nginx -V or openresty -V):
• etcd version, if have (cmd: run etcd --version):
• apisix-dashboard version, if have:
• Browser version, if have:

Additional context

No response