test(plugins): add test cases for loading manifest data

.devcontainer/devcontainer.json

modules/Plugins/Core/BasePlugin.php

modules/Plugins/Manifest/Manifest.php

modules/Plugins/Manifest/ManifestObject.php

modules/Plugins/Manifest/Person.php

tests/_support/Database/Seeds/FakeSinglePodcastApiSeeder.php

tests/modules/Api/Rest/V1/EpisodeTest.php

tests/modules/Api/Rest/V1/PodcastTest.php

tests/modules/Plugins/ManifestTest.php

tests/modules/Plugins/Mocks/manifests/manifest-empty.json

...odules/Plugins/Mocks/manifests/manifest-full-invalid.json

.../modules/Plugins/Mocks/manifests/manifest-full-valid.json

tests/modules/Plugins/Mocks/manifests/manifest-required.json

...ules/Plugins/Mocks/plugins/acme/hello-universe/Plugin.php

...s/Plugins/Mocks/plugins/acme/hello-universe/manifest.json

...modules/Plugins/Mocks/plugins/acme/hello-world/Plugin.php

...ules/Plugins/Mocks/plugins/acme/hello-world/manifest.json