Add support for Go templating in test configuration

[najose]

Adding Go templating for the configuration language along with something like sprig could make the configuration a lot more flexible and powerful. It might help us in the following ways:

• Go templates + sprig template functions opens up our configuration to use all of the default functions here https://pkg.go.dev/text/template#hdr-Functions and https://masterminds.github.io/sprig/
• We might be able to expose Terraform struct field values through templating - which may allow referencing Terraform values easily with little additional handling in infra-tester.