Rework authentication file path

From @jonas comment:

https://forum.duniter.org/t/call-for-testing-silkaj-v0-10-0rc/9187/2

authentication command

• Drop default ./authfile file path
• Save v1 auth file as user readable 600 rw------- mode, not group and world readable
  • Change to be done in DuniterPy: Store authentication files only as user readable (duniterpy#203 - closed)
  • Solved with DuniterPy v1.2 bump

Authentication

• The authentication should stop reading default ./authfile

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• Store and read authentication files into common place:
• Implement XDG Secret Service guideline