Convos does not work properly behind reverse proxy with path

**Describe the bug**
When convos is behind a reverse proxy with a path such as https://dnsname.com/convos, Convos does not work properly.

After investigating, several URL used in the web interface does not have the path. For instance:

convos request https://dnsname.com/api , where it should be https://dnsname.com/convos/api, I guess

**To Reproduce**
1. Setup apache with:

# Enable Convos to construct correct URLs by passing on custom headers.
ProxyRequests Off
ProxyPreserveHost On

RequestHeader set X-Request-Base "https://dnsname.com/convos"

# https://httpd.apache.org/docs/current/mod/mod_remoteip.html
RemoteIPHeader X-Forwarded-For

# http://httpd.apache.org/docs/2.0/mod/core.html#limitrequestbody
LimitRequestBody 0

# Pass requests on to Convos
ProxyPass /convos/events ws://localhost:3001/events
ProxyPass /convos/ http://localhost:3001/ keepalive=On
ProxyPassReverse /convos/ http://localhost:3001/convos/

2. start convos with:

`CONVOS_REQUEST_BASE="https://dnsname.com/convos/" CONVOS_REVERSE_PROXY=1 ./script/convos daemon --listen http://127.0.0.1:3001`

3. Open https://dnsname.com/convos

Convos show the login dialog but is partially loaded and does not work properly. Several HTTP resources aren't loaded and several HTTP request fail.

**Expected behavior**
Convos load all resource properly and can be used under a given http path

**Environment:**
- OS: Linux/Debian on aarch64
- Browser firefox on Linux/amd64
- Version 140.10.1esr
- IRC none (cannot login)

Start by reproducing the Apache reverse-proxy setup with the /convos path, CONVOS_REQUEST_BASE, and CONVOS_REVERSE_PROXY enabled. Inspect the generated resource and API URLs in the browser, then trace where those URLs are assembled. Done means all resources and HTTP requests retain the /convos prefix and the login flow is usable.

Written by the indexing model from the issue text.