Workaround API consistency bugs for various resources

[manicminer]

Add some helper funcs for post-deletion check and identifying key/password credentials

Increase the default retry limit by one - making it 9 retries after the first attempt for a total of 10 requests with exponential backoff

Consistency fixes for various resources:

• azuread_application_certificate: check for consistency on deletion
• azuread_application_password: check for consistency on deletion
• azuread_directory_role_member: check for consistency on deletion
• azuread_group: check for consistency on creation by attempting to patch the new group, perform consistency check on deletion
• azuread_group_member: check for consistency on deletion
• azuread_invitation: check for consistency on creation by attempting to patch the guest user, use helper func for consistency check on deletion, move flatten/expand funcs to own source file
• azuread_service_principal: check for consistency on creation by attempting to patch the new service principal, perform consistency check on deletion
• azuread_service_principal_certificate: check for consistency on deletion
• azuread_service_principal_password: check for consistency on deletion
• azuread_user: check for consistency on deletion

Note that some of these resources already attempted to PATCH themselves after creation with an empty object. It's become clear that the API is filtering these out and returning early, unless there is an actual property in the body to be changed. So now we're choosing a property to update for each resource and ensuring that a valid change is sent in the PATCH request.

Closes: #578
Closes: #611

[katbyte]

Thanks @manicminer - LGTM aside from some minor comments i've left inline 🌵

[manicminer]

Thanks @katbyte! Have tidied those up 👍

[manicminer]

Test results (failures unrelated)

[github-actions]

This functionality has been released in v2.9.0 of the Terraform Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

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[github-actions]

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