Add variable sets permission to team project

[netramali]

Description

We added a new custom permission type variable sets to team projects in atlas and hence the same needs to be done in go-tfe.

Testing plan

The integration tests pass.

External links

• JIRA

Output from tests

Including output from tests may require access to a TFE instance. Ignore this section if you have no environment to test against.

=== RUN   TestTeamProjectAccessesAdd/with_valid_options_for_all_custom_TeamProject_permissions
    --- PASS: TestTeamProjectAccessesAdd/with_valid_options_for_all_custom_TeamProject_permissions (0.87s)
PASS

=== RUN   TestTeamProjectAccessesUpdate/with_valid_custom_permissions_attributes_for_all_permissions
    --- PASS: TestTeamProjectAccessesUpdate/with_valid_custom_permissions_attributes_for_all_permissions (0.23s)
PASS