feat: add --format json support to plugin:list

Adds a `--format json` flag to `plugin:list` whose output includes each plugin's install source - for git-based third-party plugins, the git remote URL, the checked-out commit, and the followed branch - so the set of installed plugins can be reconstructed elsewhere.

Closes #8798.

plugins/plugin/Makefile

@@ -0,0 +1,11 @@
+GOARCH ?= amd64
+BUILD = plugin-list
+PLUGIN_NAME = plugin
+
+clean-plugin-list:
+	rm -rf plugin-list
+
+plugin-list: clean-plugin-list **/**/plugin-list.go
+	GOARCH=$(GOARCH) go build -ldflags="-s -w" $(GO_ARGS) -o plugin-list src/plugin-list/plugin-list.go
+
+include ../../common.mk