Add --destination support to platform local build when passthru file does not exist

[mikemilano]

When using the Drupal 7 p.sh template (and potentially others), web.locations (in .platform.app.yaml) path to index.php does not exist. As a result, Lando cannot serve the site.

_www is the default destination created by platform build however using this adds other concerns in breaking with the definitions of web.locations.

Solution

• On lando build, if web.locations./.passthru has a file defined, and that path does not exist, set the path as the --destionation value on platform local:build in psh-build.sh (line 35)
• Add p.sh destination path support to .lando.yml
  • This will be an undocumented escape hatch to override anything we've set, or cover any case we haven't

Notes

• p.sh config data in integrations/lando-platformsh/app.js -> app.platformsh
• .platform.app.yaml is parsed and set in config.js -> parseApps
• lib/run.js -> getDocRoot may work to identify the root path for 90%+ cases

If we go with passing as an argument

• 'lib/services.jsis wherehelpers/psh-build.sh` is called
  • add --destination

If we go with env vars

• Set it in types/platformsh-appserver/builder.js

[pirog]

@mikemilano long term we will eventually move to use /etc/platform/commands/build but i think that might be a post-beta activity so lets def do this for now.