External documentation is outdated - latest published version is 1.20.0

[alicejli]

The last version of this library that's been published to c.g.c. is v1.20.0 (https://cloud.google.com/java/docs/reference/google-auth-library/latest/overview). I double-checked the Cloud RAD bucket, and confirmed that v1.20.0 is the latest tarball that's been uploaded to the bucket.

This means there's something wrong with the release process for this library such that the tarball doesn't get generated/uploaded to the Cloud RAD bucket. I suspect the migration of the release jobs to Kokoro from Github likely broke this.

[alicejli]

This should be fixed for future releases with cl/617866960 and #1381. I'm exploring options for backfilling the missing docs, but it may not be possible. I'm going to mark this bug as fixed