Add metadata support to Provider VDC

[adambarreiro]

Description

This PR adds the attribute metadata_entry to the vcd_provider_vdc resource.

Solution

The difficulty of this one is the fact that vcd_provider_vdc is the only resource we have that does not have the old and deprecated metadata attribute. For that reason, this PR adapts the current code to accommodate this new casuistic:

• There's a completely new schema for resources that do not have old metadata attribute. The reason is that these don't need any Computed value (as we don't need to have both things co-living). Also the new schema takes advantage of Terraform built-ins like Required or Default that were not possible in the previous schema, also due to compatibility reasons.

• The testing framework for metadata is adapted to be able to skip the steps that test old metadata, as this does not exist in the new kind of resources.

• Other minor refactors, like function splitting, have been done.

Tests

• New tests passed on 10.5.0
• Passed: Partial metadata tests

go test -tags functional -run '^TestAcc.*Metadata' -v -timeout 0

• Passed: All metadata tests with TEST_VCD_METADATA_IGNORE=1

TEST_VCD_METADATA_IGNORE=1 go test -tags functional -run '^TestAcc.*Metadata' -v -timeout 0

• Run some manual tests: Check that ignore_metadata_changes works, try different combinations.

[Didainius]

I will trust you on running tests for whole suite, but I have attempted to use metadata_entry in vcd_provider_vdc resource and data source manually - that worked.

[adambarreiro]

I will trust you on running tests for whole suite, but I have attempted to use metadata_entry in vcd_provider_vdc resource and data source manually - that worked.

I'll probably have to re-run everything as this one clashes with #1146 😄

[dataclouder]

Full acceptance tests pass in 10.5