Add a step to cloudbuild-nomulus CB job to create a release in Cloud Deploy

[jicelhay]

This is added as the last step of the current release jobs in Cloud Build. It stores the previously computed digest for nomulus to use when creating the release.

This is safe because:

• I've verified the command manually and gave the service account cd permissions.
• The pipeline only has crash target configured + it requires manual approval to start the deployment.
• If CB fails for whatever reason, I have until monday to fix before it becomes a problem.

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This change is 

[weiminyu]

release/cloudbuild-nomulus.yaml line 191 at r1 (raw file):

    echo "Tag Name: ${TAG_NAME}"
    echo "Project ID: ${PROJECT_ID}"
    

nit: trailing whitespaces. Three more below.

Code quote:

···

[weiminyu]

@weiminyu reviewed 1 file and all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on jicelhay).

[jicelhay]

release/cloudbuild-nomulus.yaml line 191 at r1 (raw file):

Previously, weiminyu (Weimin Yu) wrote…

nit: trailing whitespaces. Three more below.

Done.

[weiminyu]

@weiminyu reviewed 1 file and all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on jicelhay).