Move add_header directives to location blocks in proxy config.

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Move the add_header directives to the location blocks in the nginx proxy config, because add_header directives in location blocks override add_header directives in the server block. See e.g. https://serverfault.com/questions/400197/add-header-directives-in-location-overwriting-add-header-directives-in-server.

Fixes #8929.

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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