Determine the version using git describe (#2388)

`v0.18.0-16-g4721f834` - the current head of my current branch is based on v0.18.0, but since it has a few commits on top of that, describe has added the number of additional commits ("16") and an abbreviated object name for the commit itself ("4721f834") at the end.

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

Makefile

@@ -25,15 +25,14 @@ TOOLS_MOD_DIR := ./internal/tools
 
 GOOS=$(shell go env GOOS)
 GOARCH=$(shell go env GOARCH)
-# BUILD_TYPE should be one of (dev, release).
-BUILD_TYPE?=release
 
-GIT_SHA=$(shell git rev-parse --short HEAD)
 BUILD_INFO_IMPORT_PATH=go.opentelemetry.io/collector/internal/version
+GIT_SHA=$(shell git rev-parse --short HEAD)
 BUILD_X1=-X $(BUILD_INFO_IMPORT_PATH).GitHash=$(GIT_SHA)
-ifdef VERSION
+VERSION=$(shell git describe --match "v[0-9]*" HEAD)
 BUILD_X2=-X $(BUILD_INFO_IMPORT_PATH).Version=$(VERSION)
-endif
+# BUILD_TYPE should be one of (dev, release).
+BUILD_TYPE?=release
 BUILD_X3=-X $(BUILD_INFO_IMPORT_PATH).BuildType=$(BUILD_TYPE)
 BUILD_INFO=-ldflags "${BUILD_X1} ${BUILD_X2} ${BUILD_X3}"