added namespace support

[dentso]

Added namespace support flag to that it works against Enterprise Vault which support namespaces. The mock vault test framework does not seem to support this feature, however I was able to test this functionality with an Enterprise Vault cluster.

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (30b3c19) 89.61% compared to head (e0cace1) 89.61%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #21 +/- ## ======================================= Coverage 89.61% 89.61% ======================================= Files 6 6 Lines 260 260 ======================================= Hits 233 233 Misses 13 13 Partials 14 14 ``` | [Flag](https://app.codecov.io/gh/kir4h/rvault/pull/21/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andr%C3%A9s+%C3%81lvarez) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/kir4h/rvault/pull/21/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andr%C3%A9s+%C3%81lvarez) | `89.61% <ø> (ø)` | | 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=Andr%C3%A9s+%C3%81lvarez#carryforward-flags-in-the-pull-request-comment) to find out more.

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[kir4h]

Thanks for your contribution and sorry for the delay in reviewing this one.

Is there something you forgot to commit? I see the changes affect the README and the viper flags, but I don´t see any logic that uses the provided namespace