Install issue

Hello, I try to install this plugin in a docker container (using dockerfile) but it`s not working.
Redis configuration is not recognized:
```2021/02/26 12:34:50 [error] 97#0: init_by_lua error: ...itnami/kong/openresty/luajit/share/lua/5.1/kong/init.lua:499: error parsing declarative config file /opt/kong.yml:
in 'services':
- in entry 2 of 'services':
in 'plugins':
- in entry 1 of 'plugins':
in 'config':
in 'redis': unknown field
stack traceback:
[C]: in function 'error'
...itnami/kong/openresty/luajit/share/lua/5.1/kong/init.lua:499: in function 'init'
init_by_lua:3: in main chunk
nginx: [error] init_by_lua error: ...itnami/kong/openresty/luajit/share/lua/5.1/kong/init.lua:499: error parsing declarative config file /opt/kong.yml:
in 'services':
- in entry 2 of 'services':
in 'plugins':
- in entry 1 of 'plugins':
in 'config':
in 'redis': unknown field
stack traceback:
[C]: in function 'error'
...itnami/kong/openresty/luajit/share/lua/5.1/kong/init.lua:499: in function 'init'
init_by_lua:3: in main chunk
Error: ...i/kong/openresty/luajit/share/lua/5.1/kong/cmd/start.lua:64: failed to start nginx (exit code: 1)
```

Configuration used:
```
plugins:
- name: proxy-cache
config:
cache_ttl: ${KONG_DICOM_METADATA_CACHE_TTL}
storage_ttl: ${KONG_DICOM_METADATA_CACHE_TTL}
response_code:
- 200
- 301
content_type:
- application/json
redis:
host: redis
port: 6379
timeout: 2000
```
In docker:
```
RUN luarocks install kong-plugin-proxy-cache
```
Plugins enabled:
```
KONG_PLUGINS: "proxy-cache,bundled,kong-response-string-replace"
```

I am using latest bitnami image bitnami/kong in DB-less mode. Any ideas ?

Thanks!