Fix sse for notifications behind nginx reverse proxy

[sdorra]

Proposed changes

Fixes SSE Events for notifications if SCM-Manager is running behind an Nginx reverse proxy. The notifications do not work behind Nginx, because Nginx buffers the response. This change will add the X-Accel-Buffering: no response header to notification subscribe endpoint. The X-Accel-Buffering: no header tells nginx to stop buffering for this endpoint.

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• PR is well described and the description can be used as a commit message on squash
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• New code is covered with unit tests
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• The clean code principles are respected (CleanCode)
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[pfeuffer]

Just change the one test method.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

95.5% Coverage
0.0% Duplication