Use header authentication for the Santa agent

[np5]

• The enrollment secret must be present as Bearer token in the Zentral-Authorization header.
• The existing URLs are deprecated and will be removed in the near future.

[np5]

The impact should be minimal. The deprecated endpoints are still present to maintain compatibility for the existing deployments.

[coveralls]

Pull Request Test Coverage Report for Build 8719759471

Details

• 16 of 17 (94.12%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.007%) to 78.496%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
zentral/contrib/santa/public_views.py	15	16	93.75%
<!--	Total:	16	17	94.12%	-->

Totals
Change from base Build 8685079049:	0.007%
Covered Lines:	35602
Relevant Lines:	45355

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💛 - Coveralls

[np5]

No issues noticed after deployment in the staging environment.