support online non-blocking garbage collection (no need to be placed in read-only mode)

[xaleeks]

We want to deliver this in 1.11, some key requirements include

• GC runs standard mark and sweep procedure and ensures nothing in use will be deleted
• GC will remove blobs(layers and manifests) from registry that are no longer referenced by an image manifest
• GC will remove untagged/dangling manifests（ie previous redis:latest sha image xxx is now replaced by image sha yyy after pushing new redis:latest, so xxx is now untagged and should get picked up by GC) - will this be part of our GC?
• can preview or ‘dry run’ GC to see how much disk space would be freed up and estimation of running time
• can run GC without setting Harbor in read-only mode, this means that user can still push / pull / delete images to that harbor instance. There is no effect to end user in terms of performing operations on Harbor and no chance of any kind of image corruption
• drastically improve the performance of GC in terms of running time
• allow manual execution as well as scheduled tasking
• allow disabling GC so it never runs
• support setting a time limit on the GC job so it never exceeds xx minutes
• provide way for harbor admin to check if GC job is running (doesn't have to be in web console)
• keeps logs of GC jobs, with each showing #blobs deleted along with their digests

[xaleeks]

https://docs.google.com/document/d/1oJpyiiTeAxC81ql6i30XpvCnn4QZEOQgtPpJQyRW-ew/edit

prd here, ping me for access

[xaleeks]

link to spec:
goharbor/community#133

[xaleeks]

link to epic tracking workstream #11534

[wy65701436]

close it as non-blocking GC is introduced in v2.1.0.