feat(live): add new datasource to query live channels

[deer-hang]

What this PR does / why we need it:

add new datasource to query live channels

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

• Tests added/passed.

make testacc TEST='./huaweicloud/services/acceptance/live' TESTARGS='-run TestAccDataSourceChannels_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud/services/acceptance/live -v -run TestAccDataSourceChannels_basic -timeout 360m -parallel 4
=== RUN   TestAccDataSourceChannels_basic
=== PAUSE TestAccDataSourceChannels_basic
=== CONT  TestAccDataSourceChannels_basic
--- PASS: TestAccDataSourceChannels_basic (12.03s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/live      12.076s

• Documentation updated.

• Schema updated.

• CheckDeleted.

  • a. During query operation (Read Context)
    aa. Resource not found
    >>>>>> Paste the screenshot here <<<<<<

  • b. During delete/disassociate/unbind operation (Delete Context)
    ba. Resource not found
    >>>>>> Paste the screenshot here <<<<<<

[github-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This PR has been approved by: @deer-hang

[github-actions]

This PR exceeds the recommended size of 1000 lines. Please make sure you are NOT addressing multiple issues with one PR. Note this PR might be rejected due to its size.

[github-actions]

This PR exceeds the recommended size of 1000 lines. Please make sure you are NOT addressing multiple issues with one PR. Note this PR might be rejected due to its size.

[github-actions]

This PR exceeds the recommended size of 1000 lines. Please make sure you are NOT addressing multiple issues with one PR. Note this PR might be rejected due to its size.

[github-actions]

This PR exceeds the recommended size of 1000 lines. Please make sure you are NOT addressing multiple issues with one PR. Note this PR might be rejected due to its size.

[jinyangyang222]

/lgtm