[RDS]: fix autoscaling

[artem-lifshits]

Summary of the Pull Request

Fix autoscaling logic and documentation.

PR Checklist

• [x] Refers to: #2628
• [x] Tests added/passed.
• [x] Documentation updated.
• [x] Schema updated.
• [x] Release notes added.

Acceptance Steps Performed

=== RUN   TestAccRdsInstanceV3Basic
--- PASS: TestAccRdsInstanceV3Basic (865.26s)
=== RUN   TestAccRdsPostgre13V3ParamsBasic
--- PASS: TestAccRdsPostgre13V3ParamsBasic (614.26s)
=== RUN   TestAccRdsInstanceV3ElasticIP
    resource_opentelekomcloud_rds_instance_v3_test.go:139: Step 2/2 error: Check failed: Check 1/2 error: opentelekomcloud_rds_instance_v3.instance: Attribute 'db.0.version' expected "10", got "15"
--- FAIL: TestAccRdsInstanceV3ElasticIP (899.73s)

=== RUN   TestAccRdsInstanceV3HA
    resource_opentelekomcloud_rds_instance_v3_test.go:170: OS_AVAILABILITY_ZONE_2 is empty
--- SKIP: TestAccRdsInstanceV3HA (0.00s)

Test ignored.
=== RUN   TestAccRdsInstanceV3OptionalParams
--- PASS: TestAccRdsInstanceV3OptionalParams (451.56s)
=== RUN   TestAccRdsInstanceV3Backup
--- PASS: TestAccRdsInstanceV3Backup (455.41s)
=== RUN   TestAccRdsInstanceV3TemplateConfig
--- PASS: TestAccRdsInstanceV3TemplateConfig (484.44s)
=== RUN   TestAccRdsInstanceV3_configurationParameters
--- PASS: TestAccRdsInstanceV3_configurationParameters (531.34s)
=== RUN   TestAccRdsInstanceV3TimeZoneAndSSL
--- PASS: TestAccRdsInstanceV3TimeZoneAndSSL (573.21s)
=== RUN   TestAccRdsInstanceV3AutoScaling
--- PASS: TestAccRdsInstanceV3AutoScaling (579.52s)
=== RUN   TestAccRdsInstanceV3RestoreToPITR
--- PASS: TestAccRdsInstanceV3RestoreToPITR (827.67s)
=== RUN   TestAccRdsInstanceV3_SSLEnable
--- PASS: TestAccRdsInstanceV3_SSLEnable (488.78s)
PASS

Process finished with the exit code 0

[artem-lifshits]

Regate

[otc-zuul[bot]]

Build succeeded. https://zuul.otc-service.com/t/eco/buildset/e467460dc6f449858799b6a8c07e1aec

:heavy_check_mark: build-otc-releasenotes SUCCESS in 3m 55s :heavy_check_mark: noop SUCCESS in 0s :heavy_check_mark: otc-golangci-lint SUCCESS in 3m 16s :heavy_check_mark: golang-make-test SUCCESS in 3m 45s :heavy_check_mark: golang-make-vet SUCCESS in 2m 41s :heavy_check_mark: tflint SUCCESS in 1m 54s :heavy_check_mark: goreleaser-build SUCCESS in 7m 04s