Add Makefile & release preparation tooling. Update README with Makefile usage.

Makefile

@@ -0,0 +1,68 @@
+export MAIN_BRANCH ?= main
+
+.DEFAULT_GOAL := help
+.PHONY: test build build/binary build/local clean test/coverage release/prepare release/tag .check_bump_type .check_git_clean help
+
+GIT_BRANCH := $(shell git symbolic-ref --short HEAD)
+WORKTREE_CLEAN := $(shell git status --porcelain 1>/dev/null 2>&1; echo $$?)
+SCRIPTS_DIR := $(CURDIR)/scripts
+
+versionFile = $(CURDIR)/.VERSION
+curVersion := $(shell cat $(versionFile) | sed 's/^v//')
+
+OPERATOR_NAME := onepassword-connect-operator
+DOCKER_IMG_TAG ?= $(OPERATOR_NAME):v$(curVersion)
+
+test:	## Run test suite
+	go test ./...
+
+test/coverage:	## Run test suite with coverage report
+	go test -v ./... -cover
+
+build:	## Build operator Docker image
+	@docker build -f Dockerfile --build-arg operator_version=$(curVersion) -t $(DOCKER_IMG_TAG)
+	@echo "Successfully built and tagged image."
+	@echo "Tag: $(DOCKER_IMG_TAG)"
+
+build/local:	## Build local version of the operator Docker image
+	@docker build -f Dockerfile -t local/$(DOCKER_IMG_TAG)
+
+build/binary: clean	## Build operator binary
+	@mkdir -p dist
+	@go build -mod vendor -a -o manager ./cmd/manager/main.go
+	@mv manager ./dist
+
+clean:
+	rm -rf ./dist
+
+help:	## Prints this help message
+	@grep -E '^[\/a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'
+
+
+## Release functions =====================
+
+release/prepare: .check_git_clean	## Updates changelog and creates release branch (call with 'release/prepare version=<new_version_number>')
+
+	@test $(version) || (echo "[ERROR] version argument not set."; exit 1)
+	@git fetch --quiet origin $(MAIN_BRANCH)
+
+	@echo $(version) | tr -d '\n' | tee $(versionFile) &>/dev/null
+
+	@NEW_VERSION=$(version) $(SCRIPTS_DIR)/prepare-release.sh
+
+release/tag: .check_git_clean	## Creates git tag
+	@git pull --ff-only
+	@echo "Applying tag 'v$(curVersion)' to HEAD..."
+	@git tag --sign "v$(curVersion)" -m "Release v$(curVersion)"
+	@echo "[OK] Success!"
+	@echo "Remember to call 'git push --tags' to persist the tag."
+
+## Helper functions =====================
+
+.check_git_clean:
+ifneq ($(GIT_BRANCH), $(MAIN_BRANCH))
+	@echo "[ERROR] Please checkout default branch '$(MAIN_BRANCH)' and re-run this command."; exit 1;
+endif
+ifneq ($(WORKTREE_CLEAN), 0)
+	@echo "[ERROR] Uncommitted changes found in worktree. Address them and try again."; exit 1;
+endif