Feat(build): fix Makefile when building on MacOS

macos default `date` command doesn't seem to have the
`--rfc-3339=date` flag. So this switches to a presumably more
universal format string.

also adds the ability to override the default `DST` to `~/$(BIN)`
directories other than ~/.bin, and pulls shared commands into Make variables.

Makefile

@@ -1,7 +1,12 @@
+DATE    := $$(date +%Y-%m-%dT%T%z)
+VERSION := $$(git describe --tags)
+COMMIT  := $$(git rev-list -1 HEAD)
+DST     ?= ~/.bin/
+
 default:
-	go build -ldflags "-X main.GitCommit=$$(git rev-list -1 HEAD) -X main.Version=$$(git describe --tags) -X main.Date=$$(date --rfc-3339=date)"
+	go build -ldflags "-X main.GitCommit=$(COMMIT) -X main.Version=$(VERSION) -X main.Date=$(DATE)"
 
 copy:
-	go build -ldflags "-X main.GitCommit=$$(git rev-list -1 HEAD) -X main.Version=$$(git describe --tags) -X main.Date=$$(date --rfc-3339=date)" && cp ./terraform-lsp ~/.bin/ && cp ./terraform-lsp ~/
+	go build -ldflags "-X main.GitCommit=$(COMMIT) -X main.Version=$(VERSION) -X main.Date=$(DATE)" && cp ./terraform-lsp $(DST) && cp ./terraform-lsp ~/
 
 .PHONY: copy