Add proboctl internal admin CLI with cookie-banner set-branding command

New staff-only CLI that connects directly to PostgreSQL (via PG_*
env vars) to manage parameters not exposed through the public API.
First command: proboctl cookie-banner set-branding <id> <true|false>

Signed-off-by: Émile Ré <emile@getprobo.com>

GNUmakefile

@@ -50,6 +50,9 @@ PROBOD_SRC=	cmd/probod/main.go
 PRB_BIN=	bin/prb
 PRB_SRC=	cmd/prb/main.go
 
+PROBOCTL_BIN=	bin/proboctl
+PROBOCTL_SRC=	cmd/proboctl/main.go
+
 PROBOD_BOOTSTRAP_BIN=	bin/probod-bootstrap
 PROBOD_BOOTSTRAP_SRC=	cmd/probod-bootstrap/main.go
 
@@ -149,7 +152,7 @@ coverage-combined: coverage-report test-e2e-coverage ## Generate combined covera
 	$(GO) tool cover -html=coverage-combined.out -o=coverage-combined.html
 
 .PHONY: build
-build: bin/probod bin/prb bin/probod-bootstrap
+build: bin/probod bin/prb bin/proboctl bin/probod-bootstrap
 
 CFG_DEV_OAUTH2_KEY = cfg/.dev-oauth2-signing-key.pem
 DEV_ENV            = .env
@@ -236,6 +239,10 @@ bin/probod: pkg/server/api/connect/v1/schema/schema.go \
 bin/prb:
 	$(GO_BUILD) -o $(PRB_BIN) $(PRB_SRC)
 
+.PHONY: bin/proboctl
+bin/proboctl:
+	$(GO_BUILD) -o $(PROBOCTL_BIN) $(PROBOCTL_SRC)
+
 .PHONY: bin/probod-bootstrap
 bin/probod-bootstrap:
 	$(GO_BUILD) -o $(PROBOD_BOOTSTRAP_BIN) $(PROBOD_BOOTSTRAP_SRC)