[MdProxy] Read secret attribute

[salv-orlando]

The NSX API returns the metadata secret and therefore it should be parsed by the read function.

This change also amends the import test to remove the ignore statement for the secret attribute.

[vmwclabot]

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• Commit 6fd773e4e7829f8139569e9ac27b98a852fba41a must be signed by [email protected]

[salv-orlando]

/test-all

[salv-orlando]

Failure for lm-3.2.3 job occurred in TestAccResourceNsxtEdgeCluster_basic which is not related to this PR.