x/build/cmd/relui: ability to make minor release announcement tweets via Twitter API

[dmitshur]

During the minor release process, towards the end, an announcement tweet is posted. For example, https://twitter.com/golang/status/1414721238224838666. (The tweet text and image are generated via a template.)

This task is to write Go code that uses the Twitter API to create a tweet with the following inputs:

• random seed (to select emoji)
• Go versions (e.g., 1.16.6 and 1.15.14)
• link to a golang-announcement mail
• GOOS, GOARCH selection for the tweet image

It can be integrated into relui as part of #47402.

[gopherbot]

Change https://golang.org/cl/358899 mentions this issue: cmd/releasebot: add modes for making a release tweet programmatically

[gopherbot]

Change https://golang.org/cl/358897 mentions this issue: internal/task: add task to tweet about Go releases

[gopherbot]

Change https://golang.org/cl/358898 mentions this issue: internal/task: post tweets via Twitter API

[gopherbot]

Change https://go.dev/cl/388834 mentions this issue: internal/task: switch to opentype for TTF font rendering

[gopherbot]

Change https://go.dev/cl/388835 mentions this issue: internal/task: update to stackblur v1.1.0