FhirIO should support conditional create / update methods

There are many use cases where it is expected that calling executeBundles in a distributed environment may fail (e.g. trying to create a resource that already exists).
We should add classes to support the following methods as implementations of FhirIO.Write to provide more robust reconciliation strategies for Dead Letter Queues involving FhirIO.Write

https://cloud.google.com/healthcare/docs/reference/rest/v1beta1/projects.locations.datasets.fhirStores.fhir/conditionalUpdate
https://cloud.google.com/healthcare/docs/reference/rest/v1beta1/projects.locations.datasets.fhirStores.fhir/create
https://cloud.google.com/healthcare/docs/reference/rest/v1beta1/projects.locations.datasets.fhirStores.fhir/update

Imported from Jira [BEAM-9990](https://issues.apache.org/jira/browse/BEAM-9990). Original Jira may contain additional context.
Reported by: data-runner0.

Start at the FhirIO.Write entry point and the executeBundles flow, then review the linked Cloud Healthcare API documentation for conditionalUpdate, create, and update. Done means FhirIO.Write implementations support these methods and provide the requested reconciliation strategies for distributed execution and dead-letter queues.

Written by the indexing model from the issue text.