Add support for new Azure Database for MySQL - Flexible Server resource

[supertrampr]

Due to upcoming changes on classic Azure Database for MySQL deployment (see this for reference), I would like to contribute on terratest examples and code for interacting and testing new available resources azurerm_mysql_flexible_server and azurerm_mysql_flexible_database.

Integration would not be so difficult in my opinion since management of the new resource expose quite similar elements to its predecessor so I think that this would not create any breaking changes (but let me know if I am missing something that I am not thinking about!)

I was not able to find anything related to this yet so I would like to contribute together on this :) Just wanted to ask if there is any constraint on what AzureRM provider and azure-sdk-for-go version to use or if I am free to use the latest version.
Out of curiosity I have already tested the example on my local environment using for both of them the latest version possible (for azurerm provider I was using constraint syntax "~>")

EDIT: A complication that I noticed is that the azure-sdk-for-go that Terratest use is very old and does not expose the needed method for the above mentioned resources until version 57.1.0 so it would be a huge jump for Terratest azure packages. Let me know if I have to file a related issue to this to ask for an upgrade on Terratest go.mod file!

Also I am new to contributing at open source project so let me know if I missed something out on this issue.

[denis256]

Hello,
changes can be separated into multiple steps:

• azure-sdk-for-go dependencies upgrade
• implementation of new Azure Database for MySQL

Will be great if backward compatibility will be kept between upgrades

[supertrampr]

Hello, changes can be separated into multiple steps:

• azure-sdk-for-go dependencies upgrade
• implementation of new Azure Database for MySQL

Will be great if backward compatibility will be kept between upgrades

Yes, I'll check but as far as I know Azure MySQL Single Server will be dismissed on 2024 and the sdk is being updated in parallel with both resource... If is it what you meant and this answer your concern :) Anyway I'll test on my side if upgrading to at least the minimum version required to have flexible servers would not break any other azure component. Thanks for your reply I'll get back to you as soon as I have some updates! Thanks @denis256 I am very glad to be of some kind of help on this

[supertrampr]

Hey @denis256, just opened pull request #1245. Let me know if there is something I need to change from my part!