Make updating Travis configurations easier

[desrosj]

Currently, there is no easy way to update Travis (and Composer?) configurations across multiple repositories.

For example, [wp-cli/wp-cli#5073]((wp-cli/wp-cli#5073) changes the default PHP version to 7.3 and introduces a test job for 7.3, but this change only takes effect on that repo. This is a change that should be reflected across all command repositories.

Ideally, there would be a way to deploy all or part of the Travis configuration automatically to the command repositories. I spot checked a handful of -command repos and the configuration files are mostly the same, ignoring a few instances where changes were not made to certain repos (using precise on 5.4, for example).

There are likely to be ways parts of the composer.json file could also be automated.

This was briefly discussed today in the #cli Slack and https://github.com/mixu/gr was brought up.

[schlessera]

There's now a GitHub Actions workflow that takes care of this. A centralized file like .travis.yml will go into the wp-cli/.github repository, and the GHA workflow contains a list of repositories that changes will automatically be replicated to.

See https://github.com/wp-cli/.github/blob/master/.github/workflows/sync-workflows.yml