Fix update bigquery transfer config

[obada-ab]

Dynamically add update mask for changed properties instead of having a static list of all updatable properties.

In the case of service_account_name, it is only added to the update mask if it was set to a non-null value, as service_account_name cannot be removed from a transfer config using the patch API.

Fixes hashicorp/terraform-provider-google#16033 and hashicorp/terraform-provider-google#16126

Release Note Template for Downstream PRs (will be copied)

bigquerydatatransfer: fixed an error when updating `google_bigquery_data_transfer_config` related to incorrect update masks

[modular-magician]

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[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 1 file changed, 41 insertions(+), 1 deletion(-))
Terraform Beta: Diff ( 1 file changed, 41 insertions(+), 1 deletion(-))

[modular-magician]

Tests analytics

Total tests: 3131
Passed tests 2814
Skipped tests: 316
Affected tests: 1

Action taken

Found 1 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

TestAccBigqueryDataTransferConfig

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[modular-magician]

$\textcolor{green}{\textsf{Tests passed during RECORDING mode:}}$
TestAccBigqueryDataTransferConfig[Debug log]

Rerun these tests in REPLAYING mode to catch issues

$\textcolor{green}{\textsf{No issues found for passed tests after REPLAYING rerun.}}$

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