Blt.yml missing drush section

[ba66e77]

Describe the bug
The blt.yml file in 12.0.0 is missing the drush section which appeared in previous versions. As a result, drupal install fails to run when deploying builds through Pipelines, which invokes the drupal install command:

On initial install, it has only two lines.

project:
  machine_name: drupal-recommended-project

To Reproduce
Steps to reproduce the behavior, ideally starting from a fresh install of BLT:

1. Run composer create-project acquia/drupal-recommended-project --no-interaction
2. Set up Pipelines
3. Trigger a build
4. See error

Expected behavior
My site builds, the Age of Aquarius dawns, lions lie down with lambs, and my cell phone plays the music of the spheres.

Detailed error output
The Pipelines error log shows ...

> drupal:install

[error]  Invalid drush alias '@${drush.aliases.ci}'. 
[info] Troubleshooting suggestions:

[info] Execute `drush site:alias` from within the docroot to see a list of available aliases.
[info] Execute `drush site:alias ${drush.aliases.ci}` for information on the @${drush.aliases.ci} alias.
[info] Execute `drush @${drush.aliases.ci} status` to determine the status of the application belonging to the alias.

[error]  Invalid drush alias '@${drush.aliases.ci}'.
For troubleshooting guidance and support, see https://docs.acquia.com/blt/support/ 

The command failed. This often indicates a problem with your configuration. Review the command output above for more detailed errors, and consider re-running with verbose output for more information.

[error]  Command `drupal:install ` exited with code 1.
For troubleshooting guidance and support, see https://docs.acquia.com/blt/support/ 

System information

• BLT version: 12.0.0

[danepowell]

@ba66e77 thanks, yesterday I noticed the same thing and put the Drush config in BLT's internal config/build.yml (which can still be overridden in blt.yml, but doesn't need to be there by default) as part of this PR: #4168

However that's blocked on something else. Maybe I need to merge just this fix sooner.