Add custom http header option when adding WebDav server for security.

[si-tech]

this is my first time for creating a pull request, thanks for reading.

floccus is a good tool for self-hosted user.

i use floccus with my self-hosted webdav server, which is running in laptop at home remotely, and use cloudflare's tunnel feature to expose the internal network. you can add custom header(token) validation for security. so if someone doesn't have right header token , she/he will not connect to this webdav server.

i want this feature added into floccus, so please check my code. some translate work is incomplete, i only translate english and my mother tongue.

[si-tech]

the cloudflare tunnel service auth config path is :
Zero Trust —> Access controls —> Applications, create an application like app1, add a service auth police.