fix(containeranalysis): fix docs and closing of client. (#5220)
fix(containeranalysis): fix docs and closing of client. (#5220)

It was documented that the embedded grafeas client shared a connection
with the main client, but it does not and never has from looking at history.
Updated the comment but also explicitly called close on the grafeas client
when the containeranalysis client is closed.

Fixes: #5217
googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go