Upstream JWT Plugin - header name and value is not added in the request

### Where is the problem?

https://docs.konghq.com/hub/optum/kong-upstream-jwt/

### What happened?

The header name and value is not added in the request.

This line in usr/local/share/lua/5.1/kong/plugins/kong-upstream-jwt/access.lua
is not wokring!!!

**ngx.req.set_header(conf.header, build_header_value(conf, jwt))**

Any more documentations related to this?

### Plugin is enabled in Kong:

curl http://localhost:8001 -s | jq .plugins | grep kong-upstream-jwt
"kong-upstream-jwt",
"kong-upstream-jwt": true,

### What did you expect to happen?

The header name and value should be added in the request.

### Code of Conduct and Community Expectations

- [X] I agree to follow this project's Code of Conduct
- [X] I agree to abide by the Community Expectations

Start with usr/local/share/lua/5.1/kong/plugins/kong-upstream-jwt/access.lua and inspect the ngx.req.set_header(conf.header, build_header_value(conf, jwt)) call. Reproduce the plugin-enabled request described in the issue and verify that the configured header name and value are present in the upstream request.

Written by the indexing model from the issue text.