GCP: Use catalog endpoint as base when refreshing OAuth2 token

[nastra]

No description provided.

[danielcweeks]

Why aren't we doing the same thing here that we do in ADLS?

RESTUtil.resolveEndpoint(
            properties.get(CatalogProperties.URI),
            properties.get(ADLS_REFRESH_CREDENTIALS_ENDPOINT));

[nastra]

we're doing it for GCP in GCPProperties:

iceberg/gcp/src/main/java/org/apache/iceberg/gcp/GCPProperties.java

Lines 109 to 112 in 978189c

	gcsOauth2RefreshCredentialsEndpoint =
	RESTUtil.resolveEndpoint(
	properties.get(CatalogProperties.URI),
	properties.get(GCS_OAUTH2_REFRESH_CREDENTIALS_ENDPOINT));

For ADLS we're also doing the same in AzureProperties:

iceberg/azure/src/main/java/org/apache/iceberg/azure/AzureProperties.java

Lines 89 to 92 in 68f8053

	this.adlsRefreshCredentialsEndpoint =
	RESTUtil.resolveEndpoint(
	properties.get(CatalogProperties.URI),
	properties.get(ADLS_REFRESH_CREDENTIALS_ENDPOINT));

For S3 it happens in AwsClientProperties:

iceberg/aws/src/main/java/org/apache/iceberg/aws/AwsClientProperties.java

Lines 109 to 111 in 7d0395d

	this.refreshCredentialsEndpoint =
	RESTUtil.resolveEndpoint(
	properties.get(CatalogProperties.URI), properties.get(REFRESH_CREDENTIALS_ENDPOINT));