Misleading name and description for reconcile-interval-seconds flag

This may be a breaking change, so fix this on the next major release. The `reconcile-interval-seconds` flag has a misleading name and description for `time.Duration` type, remove "seconds" from flag name and description and update `netd.yaml` as well.
Note: #86 fixes the default value for the `reconcile-interval-seconds` flag.
https://github.com/GoogleCloudPlatform/netd/blob/fef8459a0dcaa45965b0119137062206963654ed/pkg/options/options.go#L40-L41
https://github.com/GoogleCloudPlatform/netd/blob/fef8459a0dcaa45965b0119137062206963654ed/netd.yaml#L100
https://github.com/GoogleCloudPlatform/netd/blob/fef8459a0dcaa45965b0119137062206963654ed/netd.yaml#L204
https://github.com/GoogleCloudPlatform/netd/blob/fef8459a0dcaa45965b0119137062206963654ed/netd.yaml#L213
https://github.com/GoogleCloudPlatform/netd/blob/fef8459a0dcaa45965b0119137062206963654ed/netd.yaml#L217