Add validation to ensure that settings.configs values are dictionaries, in order to prevent misuse

[Ryu0118]

Motivation

In our team, we previously encountered cases where settings.configs was misused by passing non-dictionary values.
However, because no error was raised, the issue went unnoticed.

Proposed Solution

This PR adds validation to ensure that all values in settings.configs are dictionaries.
For example, the following invalid configuration will now throw a SpecParsingError.invalidConfigsFormat during parsing:

settings:
  configs:
    SOME_FLAG: true

If any non-dictionary values are found, a SpecParsingError.invalidConfigsFormat is thrown during parsing.

By introducing this validation, such misconfigurations can now be detected early.

[giginet]

Could you also update CHANGELOG.md?

[Ryu0118]

Currently, the following YAML is correctly detected as invalid:

settings:
  configs:
    invalid_key: value

However, the following YAML is not detected as invalid:

targets:
  invalid_target:
    settings:
      configs:
        invalid_key: value

targets:
  valid_target1:
    type: application
    platform: iOS
  valid_target2:
    type: application
    platform: iOS

aggregateTargets:
  invalid_target:
    targets:
      - valid_target1
      - valid_target2
    settings:
      configs:
        invalid_key: value

This needs to be fixed.