Add support for labels in BigQuery jobs

[JulianUmbhau]

Currently, BigQuery jobs created through this package do not support passing labels. Adding support for labels would make it easier to track and manage jobs across teams and environments.

One way it could be done is by adding the labels as options, and sending them in the body configuration:

defaults <- list(
  bigrquery.quiet = NA,
-  bigrquery.page.size = 1e4
+  bigrquery.page.size = 1e4,
+  bigrquery.labels = NULL
)

- body <- list(configuration = list(query = query))
+ labels <- getOption("bigrquery.labels")
+ body <- list(
+   configuration = list(
+     query = query,
+     labels = labels
+   )
+ )

With a labels check and documentation and testing.