ci: log commands output when deploying angular.io to Firebase (#39596)
ci: log commands output when deploying angular.io to Firebase (#39596)

In #39470, the `deploy-to-firebase.sh` script (used to deploy AIO to
Firebase when building an upstream branch), was replaced by an
equivalent JS script. In this new `deploy-to-firebase.js` script, we
were overly aggressive with suppressing command output, which made it
hard to investigate failures ([example failing CI job][1]).

This commit updates the `deploy-to-firebase.js` script to capture
command output as usual in the CI job logs. This makes the output
similar to the one generated by the old [deploy-to-firebase.sh][2]
script ([example CI logs][3]).

One concern with capturing command output is having the value of a
secret environment variables leaked in the logs. This is not the case
here, since:
1. The secret env vars are not printed from the commands that use them.
2. CircleCI will [mask the values of secret env vars][4] in the output.

As an extra precaution (although not strictly necessary), we run `yarn`
with the `--silent` option, which avoid echoing the executed yarn
commands.

[1]: https://circleci.com/gh/angular/angular/849310
[2]: https://github.com/angular/angular/blob/3b0b7d22109c79b4dceb/aio/scripts/deploy-to-firebase.sh
[3]: https://circleci.com/gh/angular/angular/848109
[4]: https://circleci.com/docs/2.0/env-vars/#secrets-masking

PR Close #39596

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