Introduced JWT based authorization for registry communication

[johannesduesing]

Reason for this PR
The instance registry will require authentication based on JSON Web Tokens (JWTs) soon (as described here). The components of the Delphi system have to be able to generate valid JWTs based on a secret that is either passed in an environment variable or in the configuration file. They have to add the encoded token in the Authorization header of every HTTP request issued to the registry. For more information see the respective issue.

Changes in this PR

• The Crawler is now able to generate valid JWTs based on a secret specified in an environment variable (using HS256 signature algorithm)
• The Crawler sends an encoded valid JWT with every request issued to the registry

[codecov-io]

Codecov Report

Merging #35 into develop will decrease coverage by 0.06%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           develop     #35      +/-   ##
==========================================
- Coverage     8.12%   8.06%   -0.07%     
==========================================
  Files           44      45       +1     
  Lines         1169    1178       +9     
  Branches        27      33       +6     
==========================================
  Hits            95      95              
- Misses        1074    1083       +9

Impacted Files	Coverage Δ
.../crawler/instancemanagement/InstanceRegistry.scala	0% <0%> (ø)	⬆️
...wt/delphi/crawler/authorization/AuthProvider.scala	0% <0%> (ø)
...a/de/upb/cs/swt/delphi/crawler/Configuration.scala	0% <0%> (ø)	⬆️

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