UI does not function behind reverse proxy

#### Describe the bug
I've toyed with different permutations of `api.base-url` and `server.http_path_prefix`. System will not function when prefixed at `/pyroscope`

#### To Reproduce
Steps to reproduce the behavior:

1. Start Pyroscope (SHA or version)

1.4.0

2. Perform Operations(Read/Write/Others)

Configure as follows:
```yaml
server:
http_listen_port: 4040
## FMS: these don't appear to work properly for reverse proxy use in 1.4.0
http_path_prefix: /pyroscope
api:
base-url: /pyroscope
```

#### Expected behavior

Port-forward config, try to visit UI at /pyroscope. Does not work. Used both `kubectl port-forward` and `HTTPProxy` frontend, all broken.

Notably, I can visit `/pyroscope/ready` and it functions. Not sure about other API endpoints.

#### Environment

- Infrastructure: Kubernetes configured with `config.yaml` mapped via ConfigMap
- Deployment tool: Helm

#### Additional Context

n/a