go mod: Allowlist specific hashicorp modules

Due to [1] We need to make sure not to use BSL modules.

Luckily the current we use have not changed.
The ones that are not changed are SDK/API and general Go libraries.
"HashiCorp APIs, SDKs, and almost all other libraries will remain MPL 2.0." [1] [2]

This commit creates a github action which allowlists them.
Any other module of hashicorp will be rejected, and will need
to be manually examined if it uses MPL (or other non restrictive license)
or BSL.

[1] https://www.hashicorp.com/blog/hashicorp-adopts-business-source-license
[2] cncf/foundation#617 (comment)

Signed-off-by: Or Shoval <oshoval@redhat.com>

.github/workflows/check_hashicorp_modules.yaml

@@ -0,0 +1,52 @@
+name: Check HashiCorp Modules
+on: [push, pull_request]
+jobs:
+  check_modules:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v2
+    - name: Run script
+      run: |
+        allowed_hashicorp_modules=(
+            "github.com/hashicorp/consul/api"
+            "github.com/hashicorp/consul/sdk"
+            "github.com/hashicorp/errwrap"
+            "github.com/hashicorp/hcl"
+            "github.com/hashicorp/logutils"
+            "github.com/hashicorp/mdns"
+            "github.com/hashicorp/memberlist"
+            "github.com/hashicorp/serf"
+            "github.com/hashicorp/go-cleanhttp"
+            "github.com/hashicorp/go-immutable-radix"
+            "github.com/hashicorp/golang-lru"
+            "github.com/hashicorp/go-msgpack"
+            "github.com/hashicorp/go-multierror"
+            "github.com/hashicorp/go.net"
+            "github.com/hashicorp/go-retryablehttp"
+            "github.com/hashicorp/go-rootcerts"
+            "github.com/hashicorp/go-sockaddr"
+            "github.com/hashicorp/go-syslog"
+            "github.com/hashicorp/go-uuid"
+            "github.com/hashicorp/go-version"
+        )
+
+        error_found=false
+        while read -r line; do
+            module=$(echo "$line" | cut -d ' ' -f 1)
+            if [[ $module == github.com/hashicorp/* ]]; then
+                if ! [[ " ${allowed_hashicorp_modules[*]} " == *" $module "* ]]; then
+                    echo "found non allowlisted hashicorp module: $module"
+                    error_found=true
+                fi
+            fi
+        done < go.sum
+
+        if [[ $error_found == true ]]; then
+            echo "Non allowlisted hashicorp modules found, exiting with an error."
+            echo "HashiCorp adapted BSL, which we cant use on our projects."
+            echo "Please review the licensing, and either add it to the list if it isn't BSL,"
+            echo "or use a different library."
+            exit 1
+        fi
+        echo "All included hashicorp modules are allowlisted"