ddev get should ignore specified yaml files that don't exist, fixes #4774

[rfay]

The Issue

• Don't fail when reading nonexistent yaml file #4774

How This PR Solves The Issue

Warn, but don't fail, on missing .platform (or other) yaml files mentioned in install.yaml

Manual Testing Instructions

• Remove .platform/routes.yaml and then ddev get ddev/ddev-platformsh. ddev start. Make sure things work.

[github-actions]

Download the artifacts for this pull request:

• all-ddev-executables.zip
• ddev-linux-amd64.zip
• ddev-linux-arm64.zip
• ddev-macos-amd64.zip
• ddev-macos-arm64.zip
• ddev-windows-amd64-installer.zip

[rfay]

See

• Improve $PLATFORM_ROUTES to include at least route id and multiple routes, for #95, followup to #47 ddev-platformsh#103

Use that for testing.

[rfay]

This actually works correctly.

I added to the install.yaml in ddev-platformsh (locally)

yaml_read_files:
  platformapp: .platform.app.yaml
  services: .platform/services.yaml
  routes: .platform/routes.yaml
  something: .platform/something.yaml

and ddev get ../ddev-platformsh showed
unable to import yaml file /Users/rfay/workspace/platform-d9mariadb/.platform/something.yaml: unable to read file /Users/rfay/workspace/platform-d9mariadb/.platform/something.yaml (open /Users/rfay/workspace/platform-d9mariadb/.platform/something.yaml: no such file or directory)

And didn't seem to cause any other trouble.