Cherry-picks of #409 and #439: Adding --http-endpoint to snapshot components

[chrishenzie]

What type of PR is this?

/kind feature

What this PR does / why we need it:
This PR contains cherry-picks of #409 and #439, which each provide an --http-endpoint flag for the snapshot-controller and csi-snapshotter.

This is already present in v4; backporting so v3 users can make use of leader election health checks and have a consistent --http-endpoint flag across the snapshot-controller and csi-snapshotter.

Does this PR introduce a user-facing change?:

The `--http-endpoint` and `--metrics-path` flags have been added to support metrics for the snapshot-controller. To enable metrics, the user must configure a `--metrics-path` such as `:9102`. The default value for `--metrics-path` is the empty string, meaning this feature is disabled by default. The default value for `--metrics-path` is `/metrics`.
Added leader election health check at the metrics port + path "/healthz/leader-election".
klog/v2 is used for logging
The `--metrics-address` flag is deprecated and replaced by `http-endpoint`, which enables handlers from both metrics manager and leader election health check.

/assign @xing-yang

I copied over the release notes from the two PRs.

[xing-yang]

The following PR should be cherry-picked as well:
#497

It's fine to submit a follow-up for that.

[xing-yang]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chrishenzie, xing-yang

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