build: update build configuration to use internal metadata package and improve ldflags injection, fix defer resp.Body.Close() usage, replace os.Setenv with t.Setenv in tests, correct error message casing, and adjust Dockerfile and Makefile for cmd/reloader structure

Makefile

@@ -20,10 +20,17 @@ BUILD=
 
 GOCMD = go
 GOFLAGS ?= $(GOFLAGS:)
-LDFLAGS =
 GOPROXY   ?=
 GOPRIVATE ?=
 
+# Version information for ldflags
+GIT_COMMIT ?= $(shell git rev-parse --short HEAD 2>/dev/null || echo "unknown")
+BUILD_DATE ?= $(shell date -u +"%Y-%m-%dT%H:%M:%SZ")
+LDFLAGS = -s -w \
+	-X github.com/stakater/Reloader/internal/pkg/metadata.Version=$(VERSION) \
+	-X github.com/stakater/Reloader/internal/pkg/metadata.Commit=$(GIT_COMMIT) \
+	-X github.com/stakater/Reloader/internal/pkg/metadata.BuildDate=$(BUILD_DATE)
+
 ## Location to install dependencies to
 LOCALBIN ?= $(shell pwd)/bin
 $(LOCALBIN):
@@ -97,10 +104,10 @@ install:
 	"$(GOCMD)" mod download
 
 run:
-	go run ./main.go
+	go run ./cmd/reloader
 
 build:
-	"$(GOCMD)" build ${GOFLAGS} ${LDFLAGS} -o "${BINARY}"
+	"$(GOCMD)" build ${GOFLAGS} -ldflags '${LDFLAGS}' -o "${BINARY}" ./cmd/reloader
 
 lint: golangci-lint ## Run golangci-lint on the codebase
 	$(GOLANGCI_LINT) run ./...
@@ -140,7 +147,7 @@ manifest:
 	docker manifest annotate --arch $(ARCH) $(REPOSITORY_GENERIC)  $(REPOSITORY_ARCH)
 
 test:
-	"$(GOCMD)" test -timeout 1800s -v ./...
+	"$(GOCMD)" test -timeout 1800s -v ./cmd/... ./internal/...
 
 stop:
 	@docker stop "${BINARY}"