Generate a warning if the builder and collector base version mismatch (…

…open-telemetry#30)

* Generate a warning if the builder and collector base version mismatch

* Show current default version in the warning message

internal/builder/main.go

@@ -50,6 +50,10 @@ func GenerateAndCompile(cfg Config) error {
 
 // Generate assembles a new distribution based on the given configuration
 func Generate(cfg Config) error {
+	// create a warning message for non-aligned builder and collector base
+	if cfg.Distribution.OtelColVersion != defaultOtelColVersion {
+		cfg.Logger.Info("You're building a distribution with non-aligned version of the builder. Compilation may fail due to API changes. Please upgrade your builder or API", "builder-version", defaultOtelColVersion)
+	}
 	// if the file does not exist, try to create it
 	if _, err := os.Stat(cfg.Distribution.OutputPath); os.IsNotExist(err) {
 		if err := os.Mkdir(cfg.Distribution.OutputPath, 0755); err != nil {