New APIG environment resource support

[Lance52259]

What this PR does / why we need it:
In order to support APIG group binding variables and API usage, HuaweiCloud needs an environment resource.

Which issue this PR fixes:
(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)
reference: #1249

Special notes for your reviewer:

Release note:

1. New environment resource supports variables binding.
2. New related acc test.
  - unit test for name and description for updates.
3. New related document.

PR Checklist

• Tests added/passed.
• Documentation updated.
• Schema updated.

Acceptance Steps Performed

make testacc TEST='./huaweicloud/services/acceptance/apig' TESTARGS='-run=TestAccApigEnvironmentV2_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud/services/acceptance/apig -v -run=TestAccApigEnvironmentV2_basic -timeout 360m -parallel 4
=== RUN   TestAccApigEnvironmentV2_basic
=== PAUSE TestAccApigEnvironmentV2_basic
=== CONT  TestAccApigEnvironmentV2_basic

--- PASS: TestAccApigEnvironmentV2_basic (448.95s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/apig      449.007s

[ShiChangkuo]

missing ForceNew

[Lance52259]

Added missing ForceNew