v9.0.0a1

[integration]

*Core

NEW: (#7258) Support using DiracX as a backend for RPC calls

*WorkloadManagementSystem

CHANGE: (#7257) Refactor PilotLoggingAgent: download proxies at initialisation. Renew a proxy if it is about to expire.

*Resources

NEW: (#7256) Add support for loading external providers in CloudCE
NEW: (#7256) Add OpenNebula6 (XMLRPC) provider for CloudCE/libcloud

*Subsystem

FIX: (#7253) prevent AREXCE from creationg delegations each time a CE got a small and temporary issue

*docs

NEW: (#7252) add documentation about setting up DIRAC to submit pilots with tokens

*WorkloadManagement

CHANGE: (#7250) pilot submission with tokens in a multi-VO context