feat(rds/flavors): support group type parameter

[Lance52259]

What this PR does / why we need it: Support the new parameter: group_type.

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

Special notes for your reviewer:

Release note:

PR Checklist

• [x] Tests added/passed.
• [x] Documentation updated.
• [x] Schema updated.

Acceptance Steps Performed

make testacc TEST='./huaweicloud/services/acceptance/rds' TESTARGS='-run=TestAccRdsFlavorDataSource_groupType'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud/services/acceptance/rds -v -run=TestAccRdsFlavorDataSource_groupType -timeout 360m -parallel 4
=== RUN   TestAccRdsFlavorDataSource_groupType
=== PAUSE TestAccRdsFlavorDataSource_groupType
=== CONT  TestAccRdsFlavorDataSource_groupType
--- PASS: TestAccRdsFlavorDataSource_groupType (41.86s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/rds       41.929s