Add AutoGrow flag for MariaDB, MySQL and PostgreSQL

[QingqingYuan2]

Add AutoGrow flag for MariaDB, MySQL and PostgreSQL.
Also align the preview API doc with latest stable version.

Latest improvements:

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Contribution checklist:

• I have reviewed the documentation for the workflow.
• Validation tools were run on swagger spec(s) and have all been fixed in this PR.
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[AutorestCI]

Automation for azure-sdk-for-ruby

Encountered a Subprocess error: (azure-sdk-for-ruby)

Command: ['/usr/local/bin/autorest', '/tmp/tmpyrkfmgtj/rest/specification/postgresql/resource-manager/readme.md', '--perform-load=false', '--swagger-to-sdk', '--output-artifact=configuration.json', '--input-file=foo', '--output-folder=/tmp/tmpomscan13']
Finished with return code 7
and output:

AutoRest code generation utility [version: 2.0.4283; node: v8.12.0]
(C) 2018 Microsoft Corporation.
https://aka.ms/autorest
Failure:
Error: Unable to start AutoRest Core from /root/.autorest/@microsoft.azure_autorest-core@2.0.4370/node_modules/@microsoft.azure/autorest-core
Error: Unable to start AutoRest Core from /root/.autorest/@microsoft.azure_autorest-core@2.0.4370/node_modules/@microsoft.azure/autorest-core
    at main (/opt/node_modules/autorest/dist/app.js:232:19)
    at <anonymous>

/root/.autorest/@microsoft.azure_autorest-core@2.0.4370/node_modules/@microsoft.azure/autorest-core/dist/app.js:33
    autorest_core_1.Shutdown();
    ^
ReferenceError: autorest_core_1 is not defined
    at process.on (/root/.autorest/@microsoft.azure_autorest-core@2.0.4370/node_modules/@microsoft.azure/autorest-core/dist/app.js:33:5)
    at emitOne (events.js:121:20)
    at process.emit (events.js:211:7)
    at process.emit (/node_modules/source-map-support/source-map-support.js:439:21)
fs.js:612
  return binding.close(fd);
                 ^

Error: EBADF: bad file descriptor, close
    at Object.fs.closeSync (fs.js:612:18)
    at StaticVolumeFile.shutdown (/opt/node_modules/autorest/dist/static-loader.js:352:10)
    at StaticFilesystem.shutdown (/opt/node_modules/autorest/dist/static-loader.js:406:17)
    at process.exit.n [as exit] (/opt/node_modules/autorest/dist/static-loader.js:169:11)
    at printErrorAndExit (/node_modules/source-map-support/source-map-support.js:423:11)
    at process.emit (/node_modules/source-map-support/source-map-support.js:435:16)
    at process._fatalException (bootstrap_node.js:391:26)

[AutorestCI]

Automation for azure-sdk-for-python

A PR has been created for you:
Azure/azure-sdk-for-python#5208

[AutorestCI]

Automation for azure-sdk-for-js

A PR has been created for you:
Azure/azure-sdk-for-js#2962

[AutorestCI]

Automation for azure-sdk-for-go

A PR has been created for you:
Azure/azure-sdk-for-go#4788

[azuresdkci]

Can one of the admins verify this patch?

[AutorestCI]

Automation for azure-sdk-for-java

A PR has been created for you:
Azure/azure-sdk-for-java#3632