[RDS] AZ switchover and backup strategy fix in resource/opentelekomcloud_rds_instance_v3

[anton-sidelnikov]

Summary of the Pull Request

Now storing azs info in availability_zones param instead of availability_zone which is with forceNew flag.

Also added workaround for https://jira.tsi-dev.otc-service.com/browse/BM-2388.

PR Checklist

• Refers to: [RDS] Failover/Switchover in OTC makes DB to be re-created #2191
• Tests added/passed.
• Documentation updated.
• Schema updated.
• Release notes added.

Acceptance Steps Performed

=== RUN   TestAccRdsInstanceV3Basic
--- PASS: TestAccRdsInstanceV3Basic (813.42s)
=== RUN   TestAccRdsPostgre13V3ParamsBasic
--- PASS: TestAccRdsPostgre13V3ParamsBasic (575.98s)
=== RUN   TestAccRdsInstanceV3RestoreBackup
--- PASS: TestAccRdsInstanceV3RestoreBackup (1015.33s)
=== RUN   TestAccRdsInstanceV3ElasticIP
--- PASS: TestAccRdsInstanceV3ElasticIP (472.32s)
=== RUN   TestAccRdsInstanceV3HA
--- PASS: TestAccRdsInstanceV3HA (383.51s)
=== RUN   TestAccRdsInstanceV3OptionalParams
--- PASS: TestAccRdsInstanceV3OptionalParams (385.60s)
=== RUN   TestAccRdsInstanceV3Backup
--- PASS: TestAccRdsInstanceV3Backup (393.61s)
=== RUN   TestAccRdsInstanceV3TemplateConfig
--- PASS: TestAccRdsInstanceV3TemplateConfig (541.17s)
=== RUN   TestAccRdsInstanceV3InvalidDBVersion
--- PASS: TestAccRdsInstanceV3InvalidDBVersion (9.30s)
=== RUN   TestAccRdsInstanceV3InvalidFlavor
--- PASS: TestAccRdsInstanceV3InvalidFlavor (9.80s)
=== RUN   TestAccRdsInstanceV3_configurationParameters
--- PASS: TestAccRdsInstanceV3_configurationParameters (513.40s)

[otc-zuul]

Build succeeded.
https://zuul.otc-service.com/t/eco/buildset/8afbb0df267c494ab84868baee86bc62

✔️ build-otc-releasenotes SUCCESS in 4m 41s
✔️ otc-golangci-lint SUCCESS in 4m 00s
✔️ golang-make-test SUCCESS in 4m 27s
✔️ golang-make-vet SUCCESS in 3m 38s
✔️ tflint SUCCESS in 2m 53s
✔️ goreleaser-build SUCCESS in 8m 01s