Add VMC Oauth app support

[wsquan171]

This change adds support of NSX token exchange on VMC using Oauth app, which is a newer method compared to using refresh token.

Implementation mainly referenced python client for vmc on aws and terraform vmc provider.

Testing done:
With Oauth app created in server-to-server mode, assigned with all roles under "VMware Cloud on AWS" category, provider configured as:

provider "nsxt" {
  host                 = "<nsx-private-ip>.rp.vmwarevmc.com/vmc/reverse-proxy/api/orgs/<org-id>/sddcs/<ssdc-id>/sks-nsxt-manager"
  allow_unverified_ssl = true
  max_retries          = 2
 
  enforcement_point    = "vmc-enforcementpoint"
  vmc_client_id        = "<oauth-app-id>"
  vmc_client_secret    = "<oauth-app-secret>"
}

Able to create and delete resources like:

resource "nsxt_policy_gateway_qos_profile" "test" {
  display_name        = "test"
  description         = "Terraform provisioned profile"
  burst_size          = 10
  committed_bandwidth = 20
}

For regression, verified using access token to create and delete the same resource. The provider is configured as follows:

provider "nsxt" {
  host                 = "<nsx-private-ip>.rp.vmwarevmc.com/vmc/reverse-proxy/api/orgs/<org-id>/sddcs/<ssdc-id>/sks-nsxt-manager"
  allow_unverified_ssl = true
  max_retries          = 2
 
  enforcement_point    = "vmc-enforcementpoint"
  vmc_token            = "<access-token>"
}

e2e test covers non-vmc cases.

Closes #944

[wsquan171]

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[wsquan171]

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[wsquan171]

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[wsquan171]

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