[BigQueryIO] support MicrosInstant type (for xlang)

[ahmedabu98]

tl;dr just adding some missing logic to support converting BQ timestamp type --> Java logical timestamp type --> Python timestamp type

We have some existing Schema translation between Python and Java SDKs for Timestamps. A Python Timestamp maps to a Java MicrosInstant (aka SqlTypes.TIMESTAMP)

Writing timestamps to BQ Storage Write API with the Python SDK works fine, but when a row fails and we try converting the BQ type back to a MicrosInstant, we get the following error:

java.lang.UnsupportedOperationException: Converting BigQuery type 'class java.lang.String' to 'LOGICAL_TYPE<beam:logical_type:micros_instant:v1> NOT NULL' is not supported
	at org.apache.beam.sdk.io.gcp.bigquery.BigQueryUtils.toBeamValue(BigQueryUtils.java:802)
	at org.apache.beam.sdk.io.gcp.bigquery.BigQueryUtils.lambda$toBeamRow$6(BigQueryUtils.java:693)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197)
	at java.base/java.util.Collections$2.tryAdvance(Collections.java:5073)
	at java.base/java.util.Collections$2.forEachRemaining(Collections.java:5081)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
	at org.apache.beam.sdk.io.gcp.bigquery.BigQueryUtils.toBeamRow(BigQueryUtils.java:694)

We're just missing some logic that accounts for when we want to convert a BQ timestamp to a MicrosInstant. I believe this was neglected because MicrosInstant isn't meant to be used as a Java native type.