Use base64 encoding

[regadas]

Fixes #3000

[codecov]

Codecov Report

Merging #3003 into master will decrease coverage by 2.65%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3003      +/-   ##
==========================================
- Coverage   72.72%   70.07%   -2.66%     
==========================================
  Files         225      225              
  Lines        7498     7498              
  Branches      326      301      -25     
==========================================
- Hits         5453     5254     -199     
- Misses       2045     2244     +199     

Impacted Files	Coverage Δ
...a/com/spotify/scio/extra/bigquery/ToTableRow.scala	85.71% <ø> (ø)
...scala/com/spotify/scio/bigquery/client/Cache.scala	0.00% <0.00%> (-74.08%)	⬇️
.../spotify/scio/bigquery/client/BigQueryConfig.scala	0.00% <0.00%> (-70.59%)	⬇️
.../spotify/scio/bigquery/BigQueryPartitionUtil.scala	0.00% <0.00%> (-52.50%)	⬇️
...scala/com/spotify/scio/bigquery/BigQueryUtil.scala	50.00% <0.00%> (-50.00%)	⬇️
...otify/scio/bigquery/syntax/ScioContextSyntax.scala	19.35% <0.00%> (-41.94%)	⬇️
...la/com/spotify/scio/bigquery/client/QueryOps.scala	0.73% <0.00%> (-39.71%)	⬇️
.../scala/com/spotify/scio/bigquery/StorageUtil.scala	0.00% <0.00%> (-36.85%)	⬇️
...com/spotify/scio/bigquery/types/BigQueryType.scala	58.33% <0.00%> (-29.17%)	⬇️
...la/com/spotify/scio/bigquery/client/TableOps.scala	0.00% <0.00%> (-25.00%)	⬇️
... and 5 more

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