[Feature Request] New load balancer data source supported

[Lance52259]

What this PR does / why we need it:

• According to Huaweicloud issue [Feature request] [ELB] Data sources for huaweicloud_elb_loadbalancer ressource  #1107, the new load balancer data source is now supported.
• Support single or multiple query of the following parameters:
  • region
  • name
  • id
  • status
  • description
  • vip_address
  • vip_subnet_id
  • enterprise_project_id

Which issue this PR fixes:
(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)
fixes #1107

Special notes for your reviewer:

Release note:

1. support new load balancer data source to fetching specifies load balancer.
2. support new load balancer acc test.
3. support new load balancer document.

PR Checklist

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

Acceptance Steps Performed

make testacc TEST='./huaweicloud' TESTARGS='-run=TestAccELBV2LoadbalancerDataSource_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud -v -run=TestAccELBV2LoadbalancerDataSource_basic -timeout 360m -parallel 4
=== RUN   TestAccELBV2LoadbalancerDataSource_basic
=== PAUSE TestAccELBV2LoadbalancerDataSource_basic
=== CONT  TestAccELBV2LoadbalancerDataSource_basic
--- PASS: TestAccELBV2LoadbalancerDataSource_basic (55.54s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud       55.604s

[ShiChangkuo]

suggest to deprecate admin_state_up, loadbalancer_provider, security_group_ids and tenant_id