fix(dev): fix Rust toolchain check in Makefile

The `make` command inside of the Vector environment image optimizes `$(shell ...)` such that if the
command to run is simple enough, it will just call it directly without using a shell. The problem is
that the `command` command used to check if the Rust toolchain is installed is a shell builtin and,
when optimized, `make` invocations that use the `check-build-tools` target emit the following error:

    make: command: Command not found

This commit fixes the issue by using a redirect, and thus forcing `make` to use the shell.

Ref: https://stackoverflow.com/a/12991757

Signed-off-by: Hugo Hromic <hhromic@gmail.com>

Makefile

@@ -221,7 +221,7 @@ build-graphql-schema: ## Generate the `schema.json` for Vector's GraphQL API
 .PHONY: check-build-tools
 check-build-tools:
 ifneq ($(ENVIRONMENT), true)
-ifeq (, $(shell command -v cargo))
+ifeq ($(shell command -v cargo >/dev/null || echo not-found), not-found)
 	$(error "Please install Rust: https://www.rust-lang.org/tools/install")
 endif
 endif