fuse/metrics: add mountpoint metrics for ossfs

[AlbeeSo]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Add mountpoint status metrics for ossfs:

### mount_retry_count
Description: The total number of retry attempts made when mounting fails due to timeout or execution errors.

### mount_point_status
Description: The health status of the mount point, where 1 indicates healthy (successfully mounted and linked), and 0 indicates unhealthy (disconnected or not created).

### mount_point_failover_count
Description: The number of failover attempts performed to remount the mount point after a FUSE client crash or disconnection.

### last_fuse_client_exit_reason
Description: The error code or reason for the last unexpected exit of the FUSE client process.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[mowangdk]

I think we lack the necessary monitor state here. At least we also have a terminating monitor state.

[AlbeeSo]

Monitor will be terminated only when the mount-proxy mounter get a SIGTERM, so I ignore the terminating state. When the ossfs exits, handleMountResult func will lock and set the state to MonitorStateInitialized and stop the regularly checkAndUpdateMountStatus overwriting the last exit reason.

[huww98]

That means if user constantly create and mount new volumes on a node, we will have unbounded number of monitors?

[huww98]

Can we merge StartMonitoring into HandleMountSuccess? They seems always be called together.

[AlbeeSo]

it works, and HandleMountSucess will be a function of monitor-manager, and HandleMountFailure is a function of monitor (or else find it in the sync.map everytime), it seems a little strange...

[mowangdk]

/lgtm
/approve

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This pull-request has been approved by: AlbeeSo, mowangdk

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