Make OSDisk Storage Type optional

[CecileRobertMichon]

What type of PR is this?

What this PR does / why we need it: Making OS disk ManagedDisk.StorageAccountType optional as it is not actually a required field for Azure APIs.

VM sizes without "s" support both Standard HDD and Standard SSD, default is Standard HDD. VM sizes with an "s" support Premium SSD, Standard HDD and Standard SSD, defaults to Premium SSD. Some select VM sizes support Ultra SSD for data disks.

Also fixed the ephemeral OS disk flavor to use ReadOnly caching and added validation for caching types.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes partially #618

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

Make OSDisk Storage Type optional

[CecileRobertMichon]

/home/prow/go/src/sigs.k8s.io/cluster-api-provider-azure/test/e2e/azure_test.go:449
Timed out after 480.114s.
Deployment default/web-windows failed

:sigh:

[CecileRobertMichon]

/retest

[CecileRobertMichon]

/assign @nader-ziada @shysank

[nader-ziada]

great PR, just wondering about the naming

[CecileRobertMichon]

Thanks for the reviews! I have been heads down on #1323 and #1330 but will address the comments tomorrow.

[k8s-ci-robot]

@CecileRobertMichon: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-cluster-api-provider-azure-apidiff	a58e6a2	link	/test pull-cluster-api-provider-azure-apidiff

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[devigned]

With all of the individual validate${TYPE} funcs, it feels like we should have a validate method added to the types via the code generator and then just have it wired up in the webhooks. Then the webhooks can call an empty validate on the top level type and have it cascade to all of the field types.

[devigned]

Overall looks great. Just curious about the name change.

[devigned]

I'm curious about the name change. Why ManagedDiskParameters rather than ManagedDisk?

[CecileRobertMichon]

Aligns with the Azure types & makes it clear this isn't about optionally enabling managed disks but rather about how the managed disk is configured.

https://github.com/Azure/azure-sdk-for-go/blob/master/services/compute/mgmt/2021-03-01/compute/models.go#L8937

[nader-ziada]

thanks for addressing all the comments Cecile

lgtm

[shysank]

/lgtm

[nader-ziada]

/test pull-cluster-api-provider-azure-e2e-windows

[CecileRobertMichon]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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