Augment the git-http-backend from 1min to 1hour

The atlassian-process-utils libary sets a default timeout of 1min, if it is not specified by the internal caller.

For Git repository management, this results in forcing the git-http-backend to timeout after that time (1min).

Change it to a large value, 1 hour, as the process is synchronous with the user + make it configurable by a system property in FishEye: fisheye.git.http-backend-timeout.