Remove the creation of a complex cloudbuild.yaml when a simpler Dockerfile suffices.

[ivannaranjo]

When we build a Docker image to be deployed to GKE we create a cloudbuild.yaml file that only builds the image by invoking docker build on the existing Dockerfile. As it turns out gcloud already supports this directly. Instead of generating the cloudbuild.yaml we can invoke gcloud like this:

gcloud container builds submit --tag={name of the tag} {path to the published app}

This will accomplish the same, building the Docker image for the app, with less complexity.

Fixes #591

[codecov]

Codecov Report

Merging #799 into master will increase coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #799      +/-   ##
==========================================
+ Coverage   10.46%   10.47%   +<.01%     
==========================================
  Files         496      496              
  Lines       12130    12124       -6     
==========================================
  Hits         1270     1270              
+ Misses      10860    10854       -6

Impacted Files	Coverage Δ
...ogleCloudExtension.Deployment/CloudBuilderUtils.cs	0% <ø> (ø)	⬆️
...nsion/GoogleCloudExtension.GCloud/GCloudWrapper.cs	0% <0%> (ø)	⬆️
...n/GoogleCloudExtension.Deployment/GkeDeployment.cs	0% <0%> (ø)	⬆️

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[ILMTitan]

Since every parameter to GetImageTag() is found in options, would it be better to move the function into class DeploymentOptions itself?

string imageTag = options.ImageTag;

or

string imageTag = options.GetImageTag();

That would also let you get rid of class CloudBuilderUtils entirely.

[ivannaranjo]

Actually I want to keep it separate because that way creating a Docker image is not only related to GKE. I am in fact working on a private change at the moment where I need this code shared as it is, because I am just building docker images out of the project.

[ivannaranjo]

PTAL