feat: support to enable the multi-AZ mode for OBS bucket

[ShiChangkuo]

What this PR does / why we need it:

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:

add multi_az field to enable or disale the multi-AZ mode for OBS bucket.

PR Checklist

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

Acceptance Steps Performed

$ make testacc TEST='./huaweicloud' TESTARGS='-run TestAccObsBucket_'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud -v -run TestAccObsBucket_ -timeout 360m -parallel 4
=== RUN   TestAccObsBucket_basic
=== PAUSE TestAccObsBucket_basic
=== RUN   TestAccObsBucket_withEpsId
=== PAUSE TestAccObsBucket_withEpsId
=== RUN   TestAccObsBucket_multiAZ
=== PAUSE TestAccObsBucket_multiAZ
=== RUN   TestAccObsBucket_versioning
=== PAUSE TestAccObsBucket_versioning
=== RUN   TestAccObsBucket_logging
=== PAUSE TestAccObsBucket_logging
=== RUN   TestAccObsBucket_quota
=== PAUSE TestAccObsBucket_quota
=== RUN   TestAccObsBucket_lifecycle
=== PAUSE TestAccObsBucket_lifecycle
=== RUN   TestAccObsBucket_website
=== PAUSE TestAccObsBucket_website
=== RUN   TestAccObsBucket_cors
=== PAUSE TestAccObsBucket_cors
=== CONT  TestAccObsBucket_basic
=== CONT  TestAccObsBucket_quota
=== CONT  TestAccObsBucket_versioning
=== CONT  TestAccObsBucket_cors
--- PASS: TestAccObsBucket_cors (15.59s)
=== CONT  TestAccObsBucket_multiAZ
--- PASS: TestAccObsBucket_versioning (27.63s)
=== CONT  TestAccObsBucket_withEpsId
--- PASS: TestAccObsBucket_quota (28.01s)
=== CONT  TestAccObsBucket_logging
--- PASS: TestAccObsBucket_multiAZ (16.90s)
=== CONT  TestAccObsBucket_website
--- PASS: TestAccObsBucket_basic (39.32s)
=== CONT  TestAccObsBucket_lifecycle
--- PASS: TestAccObsBucket_withEpsId (15.88s)
--- PASS: TestAccObsBucket_website (16.83s)
--- PASS: TestAccObsBucket_logging (23.40s)
--- PASS: TestAccObsBucket_lifecycle (16.97s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud       56.356s