Do not override database settings

[marvil07-adapt]

Describe the bug
Extra drupal database key added on include file gets removed via override.
The default local settings file is setting the full $databases array instead of setting only the relevant key, default, which causes the problem.
PR to be added soon.

To Reproduce

1. Add a new database key 'extra' at docroot/sites/settings/local.settings.php.
2. blt setup
3. drush sqlc --database="extra"

Expected behavior
The database could be used.

Detailed error output

<em class="placeholder">Notice</em>: Undefined index: extra in <em class="placeholder">require()</em> (line <em class="placeholder">174</em> of <em class="placeholder">/app/docroot/sites/default/settings/local.settings.php</em>). <pre class="backtrace">require(&#039;/app/docroot/sites/default/settings/local.settings.php&#039;) (Line: 152)
require(&#039;/app/vendor/acquia/blt/settings/blt.settings.php&#039;) (Line: 804)
require(&#039;/app/docroot/sites/default/settings.php&#039;) (Line: 122)
Drupal\Core\Site\Settings::initialize(&#039;/app/docroot&#039;, &#039;sites/default&#039;, Object) (Line: 1064)
Drupal\Core\DrupalKernel-&gt;initializeSettings(Object) (Line: 269)
Drupal\Core\DrupalKernel::createFromRequest(Object, Object, &#039;prod&#039;, 1) (Line: 223)
Drush\Boot\DrupalBoot8-&gt;bootstrapDrupalConfiguration(Object, NULL) (Line: 293)
Drush\Boot\BootstrapManager-&gt;doBootstrap(3, 3, NULL) (Line: 493)
Drush\Boot\BootstrapManager-&gt;bootstrapMax(3) (Line: 427)
Drush\Boot\BootstrapManager-&gt;bootstrapToPhaseIndex(-2, Object) (Line: 396)
Drush\Boot\BootstrapManager-&gt;bootstrapToPhase(&#039;max&#039;, Object) (Line: 28)
Drush\Boot\BootstrapHook-&gt;initialize(Object, Object) (Line: 34)
Consolidation\AnnotatedCommand\Hooks\Dispatchers\InitializeHookDispatcher-&gt;callInitializeHook(Object, Object, Object) (Line: 27)
Consolidation\AnnotatedCommand\Hooks\Dispatchers\InitializeHookDispatcher-&gt;initialize(Object, Object) (Line: 145)
Consolidation\AnnotatedCommand\CommandProcessor-&gt;initializeHook(Object, Array, Object) (Line: 289)
Consolidation\AnnotatedCommand\AnnotatedCommand-&gt;initialize(Object, Object) (Line: 221)
Symfony\Component\Console\Command\Command-&gt;run(Object, Object) (Line: 1018)
Symfony\Component\Console\Application-&gt;doRunCommand(Object, Object, Object) (Line: 271)
Symfony\Component\Console\Application-&gt;doRun(Object, Object) (Line: 147)
Symfony\Component\Console\Application-&gt;run(Object, Object) (Line: 118)
Drush\Runtime\Runtime-&gt;doRun(Array, Object) (Line: 49)
Drush\Runtime\Runtime-&gt;run(Array) (Line: 72)
require(&#039;/app/vendor/drush/drush/drush.php&#039;) (Line: 4)
</pre>
In SqlBase.php line 106:

  Unable to load Drupal settings. Check your --root, --uri, etc.


sql:cli [--extra EXTRA] [-h|--help] [-q|--quiet] [-v|vv|vvv|--verbose] [-V|--version] [--ansi] [--no-ansi] [-n|--no-interaction] [-d|--debug] [-y|--yes] [--no] [--remote-host REMOTE-HOST] [--remote-user REMOTE-USER] [-r|--root ROOT] [-l|--uri URI] [--simulate] [--pipe] [-D|--define DEFINE] [--database [DATABASE]] [--target [TARGET]] [--db-url DB-URL] [--show-passwords] [--notify [NOTIFY]] [--xh-link XH-LINK] [--druplicon] [--] <command>