feat: Add ability to customize / upgrade terraform version

[rjerrems]

Solution to #16

[rjerrems]

@morgante @ocervell - FYI looks like the build error is related to test our needing some clean up

[ocervell]

LGTM, thanks for the quick turnaround !

[morgante]

I don't really agree with this. The Dockerfile was already parameterized, why do we need to add a layer of indirection via Terraform?

[rjerrems]

@morgante - This change allows people to customize the terraform version without having to fork the actual module to make there own copy, they can still use the CFT module from the registry / Github. Let me know if you think there is a better solution to allow this? It's very common for teams to use a specific version of terraform.

[morgante]

Can't you simply override the env variables on the build to handle that, instead of introducing templating?

[rjerrems]

So you would prefer we passed through the variables to the gcloud builds submit command? We could look into that, but it will end up functionally equivalent. If templating is flakier I am happy to investigate?

[morgante]

Yeah I think that solution might be preferable. Templating locks this into Terraform, while the env-approach lets you easily copy the Dockerfile elsewhere if need be.

[rjerrems]

I have updated now so that Cloud Build or Dockerfile can be used independently if people want and still paramaterize the versions using terraform variables. Let me know what you think @morgante

[rjerrems]

@morgante - anything holding this back from merging now?