Adjust aiohttp timeouts to 30s

[xopham]

Describe the bug Admission requests timeout after 30s. The http requests of connaisseur using aiohttp apply the default timeout of 300s: https://docs.aiohttp.org/en/stable/client_quickstart.html#timeouts As a consequence, requests that fail due to badly reachable external resources are reported as internal error "failed calling webhook (..)" which is misleading as this is not an internal error reaching Connaisseur, but a timeout of Connaisseur on requesting external resources, e.g. a bad connection and should be reported as an error by Connaisseur as such. Furthermore, the 300s timeout results in logs showing no information until 300s(-30s) after the request failed which complicates triangulation of such issues.

Expected behavior http requests should timeout after 30s as there is no need to wait for a response later than that. A bit more difficult would be to enforce below 30s to ensure Connaisseur reports the error and not that the error is reported as inability to reach connaisseur.

Related to #447