Support managing API tokens and Service Accounts

[adezxc]

Add methods for managing API tokens and Service Accounts

New public methods for token management:
*VCDClient.CreateToken,*VCDClient.GetTokenById,*VCDClient.GetAllTokens,*VCDClient.GetTokenByNameAndUsername, *VCDClient.RegisterToken , *Token.GetInitialApiToken, *Token.Delete

*Client.GetApiToken - get the structure containing the access token and the bearer token using the Service Account/API token

Public methods for service account management:
*Org.GetServiceAccountById, *Org.GetAllServiceAccounts, *Org.GetServiceAccountByName

*VCDClient.CreateServiceAccount

*ServiceAccount.Update, *ServiceAccount.Authorize, *ServiceAccount.Grant, *ServiceAccount.Refresh, *ServiceAccount.Revoke, *ServiceAccount.Delete, *ServiceAccount.GetInitialApiToken

Public OpenAPI function for sending a POST request in x-www-form-urlencoded format: client.OpenApiPostUrlEncoded

[dataclouder]

First pass

[Didainius]

A quick scan with a few notes. I will get back for a more in depth review.

[Didainius]

Thanks for it - I have left improvement comments inline

[Didainius]

Thank you for all these fixes. I am actually good now - the only remaining comment from is to see if we could use OpenApiPostItem instead of OpenApiPostUrlEncoded as they look to be very very similar (see my comment inline). Not insisting on that if it doesn't feel like a good approach.

[adambarreiro]

Great work, approved.