Support setting fs-dir for fs datasource

[jeesmon]

We had a control plane meltdown when starting KFO on a GKE cluster with 1000s of nodes as reloader will make several kube api calls at the same time when DaemonSet pods start at the same time. In order to mitigate this issue we are planning to go with fs datasource with configs read from a volume mount. But the current helm chart doesn't have an option to set required --fs-dir arg when datasource: fs is used. This PR is to add an option to set fs-dir in helm so that we can use fs datasoiurce.

[vmwclabot]

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[jeesmon]

@luisdavim Can you please review? Thanks!

[luisdavim]

LGTM, thanks.