azurerm_subnet: Remove ForceNew from default_outbound_access_enabled property.

[CorrenSoft]

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Description

Removed ForceNew flag from default_outbound_access_enabled property.
Updated TestAccSubnet_defaultOutbound to evaluate the update on the property.

Notes:

• The documentation has not been updated as it does not describe the property as Force Recreation.
• This change is not required in azurerm_virtual_network resource, since it is already supporting the update without recreation.

PR Checklist

• I have followed the guidelines in our Contributing Documentation.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• I have checked if my changes close any open issues. If so please include appropriate closing keywords below.
• I have used a meaningful PR title to help maintainers and other users understand this change and help prevent duplicate work.

Changes to existing Resource / Data Source

• I have added an explanation of what my changes do and why I'd like you to include them (This may be covered by linking to an issue above, but may benefit from additional explanation).
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Testing

• My submission includes Test coverage as described in the Contribution Guide and the tests pass. (if this is not possible for any reason, please include details of why you did or could not add test coverage)

make acctests  SERVICE='network' TESTARGS='-run=TestAccSubnet_defaultOutbound'
==> Checking that code complies with gofmt requirements...
==> Checking that Custom Timeouts are used...
==> Checking that acceptance test packages are used...
TF_ACC=1 go test -v ./internal/services/network -run=TestAccSubnet_defaultOutbound -timeout 180m -ldflags="-X=github.com/hashicorp/terraform-provider-azurerm/version.ProviderVersion=acc"
=== RUN   TestAccSubnet_defaultOutbound
=== PAUSE TestAccSubnet_defaultOutbound
=== CONT  TestAccSubnet_defaultOutbound
--- PASS: TestAccSubnet_defaultOutbound (312.60s)
PASS
ok      github.com/hashicorp/terraform-provider-azurerm/internal/services/network       312.871s

Change Log

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

• azurerm_subnet - default_outbound_access_enabled property can be updated without recreate the resource [Switching default_outbound_access_enabled from true to false for azurerm_subnet forces replacement #27848]

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 #27848

Note

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

[stephybun]

Thanks @CorrenSoft LGTM 👍