Fix tmux session handling in Makefile

Fixes #3840

Modify the `Makefile` to check for an existing tmux session named `grapher` and resume it if it exists, during `make up` or `make up.full`.

Makefile

@@ -47,6 +47,12 @@ up: export DEBUG = 'knex:query'
 up: require create-if-missing.env ../owid-content tmp-downloads/owid_metadata.sql.gz node_modules
 	@make validate.env
 	@make check-port-3306
+
+	@if tmux has-session -t grapher 2>/dev/null; then \
+		echo '==> Killing existing tmux session'; \
+		tmux kill-session -t grapher; \
+	fi
+
 	@echo '==> Building grapher'
 	yarn lerna run build
 
@@ -97,6 +103,11 @@ up.full: require create-if-missing.env.full ../owid-content tmp-downloads/owid_m
 	@make validate.env.full
 	@make check-port-3306
 
+	@if tmux has-session -t grapher 2>/dev/null; then \
+		echo '==> Killing existing tmux session'; \
+		tmux kill-session -t grapher; \
+	fi
+
 	@echo '==> Building grapher'
 	yarn lerna run build
 
@@ -299,4 +310,4 @@ local-bake: itsJustJavascript
 	yarn buildLocalBake
 
 clean:
-	rm -rf node_modules itsJustJavascript
+	rm -rf node_modules itsJustJavascript