This addresses the login issue caused by pikpak's recent cancellation
of existing login methods and requirement for additional verifications.
To resolve this, we've made the following changes:
1. Similar to lib/oauthutil, we've integrated a mechanism to handle
captcha tokens.
2. A new pikpakClient has been introduced to wrap the existing
rest.Client and incorporate the necessary headers including
x-captcha-token for each request.
3. Several options have been added/removed to support persistent
user/client identification.
* client_id: No longer configurable.
* client_secret: Deprecated as it's no longer used.
* user_agent: A new option that defaults to PC/Firefox's user agent
but can be overridden using the --pikpak-user-agent flag.
* device_id: A new option that is randomly generated if invalid.
It is recommended not to delete or change it frequently.
* captcha_token: A new option that is automatically managed
by rclone, similar to the OAuth token.
Fixes#7950#8005
48f2c2db70