add prometheus monitoring foundation

package.json

packages/rocketchat-api/package.js

packages/rocketchat-api/server/default/info.js

packages/rocketchat-api/server/default/metrics.js

packages/rocketchat-lib/.npm/package/npm-shrinkwrap.json

packages/rocketchat-lib/package.js

packages/rocketchat-lib/server/lib/metrics.js

packages/rocketchat-lib/server/methods/sendMessage.coffee