Resolve metadata-cache-ttl in new config

[kislaykishore]

Resolve metadata-cache-ttl in new config

Description

• We want to use the metadata-cache.ttl-secs field to represent the metadata-cache ttl and resolve it upfront as opposed to resolving it when needed. We'll follow up with a similar change for the old config too which will allow us to use the old and new configs interchangeably.
• Make change to set the enable-empty-managed-folders whenever enable-hns is set.

Link to the issue in case of a bug fix.

NA

Testing details

1. Manual - NA
2. Unit tests - Added the required unit tests in cmd/ in order to avoid cyclic dependency.
3. Integration tests - NA

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 15.38462% with 11 lines in your changes missing coverage. Please review.

Project coverage is 71.94%. Comparing base (43e4b64) to head (f9dc6d1).

Files	Patch %	Lines
cfg/validate.go	0.00%	11 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2099 +/- ## ======================================= Coverage 71.93% 71.94% ======================================= Files 101 102 +1 Lines 10996 11009 +13 ======================================= + Hits 7910 7920 +10 - Misses 2758 2763 +5 + Partials 328 326 -2 ``` | [Flag](https://app.codecov.io/gh/GoogleCloudPlatform/gcsfuse/pull/2099/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/GoogleCloudPlatform/gcsfuse/pull/2099/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform) | `71.94% <15.38%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GoogleCloudPlatform#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.