[BACKPORT][v1.6.1][BUG] Add Snapshot Maximum Count to the Settings

[github-actions]

backport #7906

[longhorn-io-github-bot]

Pre Ready-For-Testing Checklist

• Where is the reproduce steps/test steps documented?
  The reproduce steps/test steps are at: Install LH via helm chart without error.

• Is there a workaround for the issue? If so, where is it documented?

• Does the PR include the explanation for the fix or the feature? yes

• Does the PR include deployment change (YAML/Chart)? If so, where are the PRs for both YAML file and Chart?
  The PR for the YAML change is at: chart: Add Snapshot Maximum Count to the Settings (backport #7896) #7980
  The PR for the chart change is at: chart: Add Snapshot Maximum Count to the Settings (backport #7896) #7980

• Have the backend code been merged (Manager, Engine, Instance Manager, BackupStore etc) (including backport-needed/*)?
  The PR is at chart: Add Snapshot Maximum Count to the Settings (backport #7896) #7980

[roger-ryao]

Verified on v1.6.x-head 20240304

• longhorn v1.6.x-head 7e01ba1

The test steps

#7979 (comment)

Result Passed

• Install LH via helm chart without error.
• require/chart : Installed Longhorn using Helm chart and modified snapshotMaxCount to 150, and it took effect.