Use go tool to run protoc-gen-terraform

[hugoShaka]

This PR uses go tool to install and manage the protoc-gen-terraform plugin responsible for generating the Terraform schemas.

This provides the following benefits:

• devs don't need to manually install tools
• switching between different branches and versions is now transparent
• we track the version in a single place
• in case of repo compromise, it is impossible to install a wrong version, the go.sum will reject the install

[zmb3]

Seems fine, though you might consider following the dedicated-go.mod pattern that we have under build.assets/tools.

[hugoShaka]

Seems fine, though you might consider following the dedicated-go.mod pattern that we have under build.assets/tools.

I'm not super comfortable with the makefile crimes we're committing to do this:

teleport/common.mk

Lines 57 to 67 in 8ea6a9b

	COMMON_MK_DIR := $(dir $(lastword $(MAKEFILE_LIST)))
	# This allows $(GOTESTSUM) in any Makefile that includes common.mk:
	# TOOLS_DIR contains external test tools
	TOOLS_DIR := $(abspath $(COMMON_MK_DIR)/build.assets/tools)
	GOTESTSUM = "$$( GOWORK=off go -C $(TOOLS_DIR)/gotestsum tool -n gotestsum )"
	GCI = "$$( GOWORK=off go -C $(TOOLS_DIR)/gci tool -n gci )"
	GODA = "$$( GOWORK=off go -C $(TOOLS_DIR)/goda tool -n goda )"
	BENCHSTAT = "$$( GOWORK=off go -C $(TOOLS_DIR)/benchstat tool -n benchstat )"
	# TOOLING_DIR contains internal tooling
	TOOLING_DIR := $(abspath $(COMMON_MK_DIR)/build.assets/tooling)
	HELMJANITOR = "$$( GOWORK=off CGO_ENABLED=0 go -C $(TOOLING_DIR) tool -n helm-janitor )"

I also spent 5 hours debugging this because the hacks we did doesn't work with exported variables and make -e.
We do call make -e in some CI targets, and export every variable in the Makefile for some reason.

[backport-bot-workflows]

@hugoShaka See the table below for backport results.

Branch	Result
branch/v17	Failed
branch/v18	Failed