feat: support snapshot max count for v2 (backport #1391)

[mergify]

Which issue(s) this PR fixes:

longhorn/longhorn#12921

What this PR does / why we need it:

Special notes for your reviewer:

Additional documentation or context

---

This is an automatic backport of pull request #1391 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 1ecf693 has failed:

On branch mergify/bp/v1.12.x/pr-1391
Your branch is up to date with 'origin/v1.12.x'.

You are currently cherry-picking commit 1ecf693e.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   pkg/client/instance.go
	modified:   pkg/instance/instance.go
	modified:   pkg/proxy/volume.go
	modified:   vendor/github.com/longhorn/longhorn-spdk-engine/pkg/api/types.go
	modified:   vendor/github.com/longhorn/longhorn-spdk-engine/pkg/client/client_engine.go
	modified:   vendor/github.com/longhorn/longhorn-spdk-engine/pkg/spdk/engine.go
	modified:   vendor/github.com/longhorn/longhorn-spdk-engine/pkg/spdk/server_engine.go
	modified:   vendor/github.com/longhorn/types/pkg/generated/imrpc/instance.pb.go
	modified:   vendor/github.com/longhorn/types/pkg/generated/spdkrpc/spdk.pb.go
	modified:   vendor/github.com/longhorn/types/pkg/generated/spdkrpc/spdk_grpc.pb.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   go.mod
	both modified:   go.sum
	both modified:   vendor/modules.txt

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[derekbit]

Hello @davidcheng0922 Could you update the go.mod to use v1.12.x longhorn-spdk-engine? Thank you.

[davidcheng0922]

Hello @davidcheng0922 Could you update the go.mod to use v1.12.x longhorn-spdk-engine? Thank you.

Done, thank you

[derekbit]

https://github.com/longhorn/longhorn-spdk-engine/commits/v1.12.x/

The commit id should be a07df50fb05a43d68790e95954fd08cf3f8bdd2b