azurerm_postgresql_flexible_server: more support for in-place major version upgrade

[wuxu92]

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Description

Per API's behavior of create_mode only works when creating the instance, and upgrade the version of the server should not cause a force-recreate of the resource. I have tested locally, whether create_mode set or not, the version can be upgrade successfully. So this PR changes the force-new logic to only when downgrading the version.

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Testing

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--- PASS: TestAccPostgresqlFlexibleServer_upgradeVersion (2564.89s)
PASS
ok      github.com/hashicorp/terraform-provider-azurerm/internal/services/postg

Change Log

Below please provide what should go into the changelog (if anything) conforming to the Changelog Format documented here.

• azurerm_postgresql_flexible_server - support in-place major version upgrade [changing the azurerm_postgresql_flexible_server version from 11 to any other version forces a recreate #25184]

This is a (please select all that apply):

• Bug Fix
• New Feature (ie adding a service, resource, or data source)
• Enhancement
• Breaking Change

Related Issue(s)

Fixes #25184

Note

If this PR changes meaningfully during the course of review please update the title and description as required.

[nachoalonsoportillo]

Here's my proposal to improve this experience...

Say the user has deployed a server using this block:

resource "azurerm_postgresql_flexible_server" "example" {
  name                          = "example-psqlflexibleserver"
  resource_group_name           = azurerm_resource_group.example.name
  location                      = azurerm_resource_group.example.location
  version                       = "13"
  public_network_access_enabled = true
  administrator_login           = "myadmin"
  administrator_password        = "mypassword"
  storage_mb                    = 32768
  sku_name                      = "B_Standard_B1ms"
  zone                          = 1
  create_mode                   = "Default"
  

My proposal is that we implement some additional allow_major_version_upgrade boolean property, which must be present and set to true for the MVU to be initiated. Although the backend doesn't expect or support any equivalent property, I think it would be good to have so that users don't shoot on their own food and accidentally initiate an irreversible major version upgrade operation:

resource "azurerm_postgresql_flexible_server" "example" {
  name                          = "example-psqlflexibleserver"
  resource_group_name           = azurerm_resource_group.example.name
  location                      = azurerm_resource_group.example.location
  version                       = "15" <<<<<<<<< Bumped up the version
  public_network_access_enabled = true
  administrator_login           = "myadmin"
  administrator_password        = "mypassword"
  storage_mb                    = 32768
  sku_name                      = "B_Standard_B1ms"
  zone                          = 1
  create_mode                   = "Default"
  allow_major_version_upgrade   = true  <<<<<<<<< If value set to version property is higher than current major version on instance, and this property isn't present and set to true, the provider would raise an error requiring its presence.
}