List user's open cpython PRs, add "get info from PR" button

At PyConUS in the sprints and hoping to make some workflow improvements based on new developers using blurb. Can split into multiple issues, but high level:

1. List the most recent open CPython PRs by the user (limited to a smallish number)
2. Add a "fetch" button so given the github PR number can get information on it (github issue, if there is an existing blurb). Limit the max "fetch file" size. (This same infra used for "click on PR -> get info)
3. Be able to update an existing blurb in the PR (simple edits without having to figure out git workflow)

Happy to split into multiple smaller issues/prs. If any of these are outside scope of the blurb-it app let me know

Empieza revisando el workflow existente para hacer clic en un PR y obtener información, y después divide la solicitud en los tres workflows propuestos: listar los PRs abiertos de CPython, obtener información de un PR y actualizar un blurb existente. Confirma el alcance con los maintainers antes de definir qué significa que esté terminado, ya que el issue es explícitamente de alto nivel y pregunta si todo el trabajo solicitado pertenece a blurb-it.