Parallel automatic client registration with more than a TA

[peppelinux]

Supported in the code but it should be async with a not blocking loop

https://github.com/italia/spid-cie-oidc-django/pull/249/files#diff-16a4a049e67ec9d46a9fa09e8a60e787d060b5a0bd597cb83fe16162af4710edR75