CPLAT-13993: Read config from dart_dependency_validator.yaml if available

[evanweible-wf]

Motivation

pub publish warns when it finds unrecognized keys, which is problematic because we currently read static config from a dependency_validator entry in pubspec.yaml.

Changes

• Deprecate the current static config location within pubspec.yaml (the executable now warns when it is used)
• Add support for reading the same config format (without the dependency_validator: key) from a dart_dependency_validator.yaml file in the root of the package. This name was chosen to match the convention set by the test package using a dart_test.yaml config file.
• Tests have been updated and both the deprecated and new config codepaths are verified.

[aviary3-wk]

Security Insights

No security relevant content was detected by automated scans.

Action Items

• Review PR for security impact; comment "security review required" if needed or unsure

• Verify aviary.yaml coverage of security relevant code

  Questions or Comments? Reach out on Slack: #support-infosec.

[evanweible-wf]

QA +1

• [x] CI passes
• [x] Verified that pub publish --dry-run no longer emits any warnings

@Workiva/release-management-p