azurerm_media_streaming_endpoint - correctly support tags, sku, and scale_units

[teowa]

• fix tags
• export current_sku
• change scale_units maxmium to 50
• refactor to retrieve the existing and use d.HasChanges consistently in Update

Test:

make acctests SERVICE="media" TESTARGS="-parallel 50 -test.run=TestAccMediaStreamingEndpoint" TESTTIMEOUT='1440m' 
==> 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/media -parallel 50 -test.run=TestAccMediaStreamingEndpoint -timeout 1440m -ldflags="-X=github.com/hashicorp/terraform-provider-azurerm/version.ProviderVersion=acc"
=== RUN   TestAccMediaStreamingEndpoint_basic
=== PAUSE TestAccMediaStreamingEndpoint_basic
=== RUN   TestAccMediaStreamingEndpoint_CDN
=== PAUSE TestAccMediaStreamingEndpoint_CDN
=== RUN   TestAccMediaStreamingEndpoint_MaxCacheAge
=== PAUSE TestAccMediaStreamingEndpoint_MaxCacheAge
=== RUN   TestAccMediaStreamingEndpoint_shouldStopWhenStarted
=== PAUSE TestAccMediaStreamingEndpoint_shouldStopWhenStarted
=== RUN   TestAccMediaStreamingEndpoint_update
=== PAUSE TestAccMediaStreamingEndpoint_update
=== RUN   TestAccMediaStreamingEndpoint_standard
=== PAUSE TestAccMediaStreamingEndpoint_standard
=== CONT  TestAccMediaStreamingEndpoint_basic
=== CONT  TestAccMediaStreamingEndpoint_shouldStopWhenStarted
=== CONT  TestAccMediaStreamingEndpoint_standard
=== CONT  TestAccMediaStreamingEndpoint_MaxCacheAge
=== CONT  TestAccMediaStreamingEndpoint_CDN
=== CONT  TestAccMediaStreamingEndpoint_update
--- PASS: TestAccMediaStreamingEndpoint_standard (229.54s)
--- PASS: TestAccMediaStreamingEndpoint_MaxCacheAge (230.36s)
--- PASS: TestAccMediaStreamingEndpoint_CDN (234.82s)
--- PASS: TestAccMediaStreamingEndpoint_basic (236.53s)
--- PASS: TestAccMediaStreamingEndpoint_shouldStopWhenStarted (247.35s)
--- PASS: TestAccMediaStreamingEndpoint_update (325.54s)
PASS
ok      github.com/hashicorp/terraform-provider-azurerm/internal/services/media 325.588s

[stephybun]

Thanks @teowa LGTM 👍

[github-actions]

This functionality has been released in v3.45.0 of the Terraform Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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