feature: Allow multi snapshotters

[wangforthinker]

Ⅰ. Describe what this PR did

Add a daemon config allow-multi-snapshotter, if set true, pouchd will allow multi snapshotter.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)? (你真的觉得不需要加测试吗？)

Add test.

Ⅳ. Describe how to verify it

Add a flag allow-multi-snapshotter, if set true, pouchd will ignore check multi snapshotter snapshots.

Ⅴ. Special notes for reviews

[codecov]

Codecov Report

Merging #2631 into master will decrease coverage by 1.53%.
The diff coverage is 40%.

@@            Coverage Diff             @@
##           master    #2631      +/-   ##
==========================================
- Coverage   69.57%   68.04%   -1.54%     
==========================================
  Files         280      280              
  Lines       18844    18845       +1     
==========================================
- Hits        13111    12823     -288     
- Misses       4268     4526     +258     
- Partials     1465     1496      +31

Flag	Coverage Δ
#criv1alpha1test	31.35% <40%> (-0.05%)	⬇️
#criv1alpha2test	35.56% <40%> (-0.15%)	⬇️
#integrationtest	41.59% <40%> (-0.09%)	⬇️
#nodee2etest	?
#unittest	26.91% <0%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
daemon/config/config.go	66.21% <ø> (ø)	⬆️
daemon/daemon_utils.go	62.5% <ø> (+12.5%)	⬆️
daemon/daemon.go	68.58% <0%> (ø)	⬆️
ctrd/client.go	64.04% <41.37%> (-6.43%)	⬇️
cri/stream/remotecommand/websocket.go	0% <0%> (-81.54%)	⬇️
cri/stream/remotecommand/exec.go	36.66% <0%> (-43.34%)	⬇️
cri/ocicni/cni_manager.go	54.9% <0%> (-15.69%)	⬇️
cri/stream/remotecommand/errors.go	14.28% <0%> (-14.29%)	⬇️
cri/v1alpha2/cri_wrapper.go	53.2% <0%> (-13.6%)	⬇️
pkg/streams/utils.go	82.14% <0%> (-9.53%)	⬇️
... and 17 more

[Ace-Tang]

LGTM

[allencloud]

I left several comments. Wish to get your feedback to move on. @wangforthinker

[allencloud]

Thanks for your update again. I removed the DO-NOT-MERGE label. In addition, after the update you made, I think it is necessary for @Ace-Tang to take a review again since the code change. WDYT? @Ace-Tang
If it still satisfies you, I think we could make to make this move on to merge.

[Ace-Tang]

Look good to me, /cc @allencloud

[allencloud]

Thanks for your review. Merging... @Ace-Tang

[Ace-Tang]

PR should not be added to fixed, #2585 was closed by error