feat: add metadata to backend config generation

[katcipis]

Introduces referencing metadata on backend configuration.

Here is an example script:

#!/bin/bash

set -o errexit
set -o nounset

basedir=$(mktemp -d)

cd "${basedir}"

mkdir -p envs/prod/stack
terramate init envs/prod/stack

mkdir -p envs/staging/stack
terramate init envs/staging/stack

echo "listing stacks:"
echo

terramate list

echo

cat > envs/staging/terramate.tm.hcl <<- EOM
terramate {
  backend "gcs" {
    bucket = "the-bucket-staging"
    prefix = terramate.path
  }
}
EOM

cat > envs/prod/terramate.tm.hcl <<- EOM
terramate {
  backend "gcs" {
    bucket = "the-bucket-prod"
    prefix = terramate.path
  }
}
EOM

echo "files before code generation:"

tree

echo

echo "=== generating code ==="
echo

terramate generate

echo "files after code generation:"

tree

echo

echo "generated code for staging:"

cat envs/staging/stack/_gen_terramate.tm.tf

echo
echo "generated code for prod:"

cat envs/prod/stack/_gen_terramate.tm.tf

[i4ki]

lgtm

[i4ki]

lgtm