Implement dCache support

[mzur]

• Implement proof of concept for dcache with webdav and token exchange
• Add optional path prefix
• Extend the manual
• Add/update tests for disk storage/update
• Find a solution that does not install the haai and elements packages everywhere
• Implement a dcache storage adapter, extending the webdav adapter, that supports temporary URLs via macaroons
• Add error handling for OIDC flow and token exchange
• Implement scheduled job (each hour) to update disks with almost expiring refresh_token (<=2h)
• Find a way do lazily refresh an expired token if a disk is accessed and the refresh_token is still valid
• Implement refresh of token exchange if refresh_token is expired and user clicks on "update disk"
• Add loading spinner to "create" and "update" buttons.
• Add installation instructions for each type to the readme (required additional package, required service config).