[resultdb] BigQuery Export: Create a BQ table if it doesn't exist
[resultdb] BigQuery Export: Create a BQ table if it doesn't exist

Prep work before exporting:
- Initialize bq client
- check the existence of the table
- create it if it doesn't exist.

Bug: 1030355
Change-Id: Id9bfca21f7697ebf85d6a6fa7bac7de4358d7a43
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1982534
Commit-Queue: Chan Li <332b6c56634d0f63001046c664a2370006a02420@chromium.org>
Reviewed-by: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go