Add support of password file in loading SSL certificates

[adrysn]

Manager, Storage-Proxy, etc. supports HTTPS mode by loading SSL certificate chain. However, they cannot load the certificates encrypted with a pass phrase (password file). For more security, we are better to support the loading of SSL certificate chain with a pass phrase.

For example in Manager, the cert chain is loaded in the following lines:
https://github.com/lablup/backend.ai-manager/blob/d180e9b441b0ea95b9d4ae980191988621928019/src/ai/backend/manager/server.py#L589-L592

The load_cert_chain actually supports the password parameter, so we can just append a password file if exists. manager.toml should also support the ssl-password field under the [manager] section.

Target services: Manager, Storage-Proxy, Webserver, etc.

[xyloon]

Nginx ssl termination for webserver , wsproxy and storage-proxy example

https://github.com/lablup/backend.ai-proxy-coordinator/commit/0a0b207e72d348db3be5c8689e9fa64f846e2d50