feat: Add new and missing fields for /v4/enrollment

[neilmartin83]

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Not a 11.19 specific PR. This ensures parity between API request/response bodies and SDK types. Added back the Flush* fields as these are set by the API to false as default when omitted anyway, so this makes no difference here. Decided it was better to include them for completeness.

MaidUsernameMergeEnabled appeared in 11.16 and is useful for ADUE flows - not exposed in the GUI and gets set to false whenever anyone makes a change to UIE settings in the GUI, so an ideal candidate for TF to manage where needed...

PersonalDeviceEnrolmentType needs to be ommited if empty, or we get an API 409 error. If omitted, the API sets a default value. Was causing an issue with the UIE resource block in TF if not including that field's argument (it's optional in the provider and the API).

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