Add CatalogItem metadata support for vcd_catalog_item

[adambarreiro]

Description

This PR adds the capability of including metadata in the vcd_catalog_item resource that belongs to the CatalogItem itself, as right now the metadata attribute belongs to the associated vApp template. The new attribute for this is called catalog_item_metadata.

The data source has been also updated to fetch the CatalogItem metadata into that attribute.

Documentation and log messages have been updated accordingly.

The changes somehow relate to the issue #502

[adambarreiro]

Tested manually and works.

[lvirbalas]

Few requests, but approving in advance. Don't hesitate to resolve my comments when ready to merge this time.

[vmwclabot]

@adambarreiro, you must sign every commit in this pull request acknowledging our Developer Certificate of Origin before your changes are merged. This can be done by adding Signed-off-by: John Doe <john.doe@email.org> to the last line of each Git commit message. The e-mail address used to sign must match the e-mail address of the Git author. Click here to view the Developer Certificate of Origin agreement.

• Commit 18553b5 must be signed by abarreiro@vmware.com

[vmwclabot]

@adambarreiro, you must sign every commit in this pull request acknowledging our Developer Certificate of Origin before your changes are merged. This can be done by adding Signed-off-by: John Doe <john.doe@email.org> to the last line of each Git commit message. The e-mail address used to sign must match the e-mail address of the Git author. Click here to view the Developer Certificate of Origin agreement.

• Commit 18553b5 must be signed by abarreiro@vmware.com