Let garbage collector to save user integrations

The master server's storage is limited and for this reason there has been a design decision to protect integrations triggered only by gerrit.

For developers running private instances this sometimes wastes development time because sometimes gc will wipe out the binary artifacts that need to be rebuild for custom integrations.

Currently, this is not possible to implement because there is not enough storage space, but if we would increase storage capacity, the gc could potentially protect artifacts for all integration types.