Add support for `IndexableByKey` annotation for entity sets

[irvinesunday]

We need to add support for retrieving Org.OData.Capabilities.V1.IndexableByKey annotations for entity sets here:

OpenAPI.NET.OData/src/Microsoft.OpenApi.OData.Reader/Edm/ODataPathProvider.cs

Lines 250 to 267 in b560729

	if (entitySet != null)
	{
	string targetPath = path.GetTargetPath(_model);
	count = _model.GetRecord<CountRestrictionsType>(targetPath, CapabilitiesConstants.CountRestrictions)
	?? _model.GetRecord<CountRestrictionsType>(entitySet, CapabilitiesConstants.CountRestrictions);
	if(count?.Countable ?? true) // ~/entitySet/$count
	CreateCountPath(path, convertSettings);
	CreateTypeCastPaths(path, convertSettings, entityType, entitySet, true); // ~/entitySet/subType
	if (convertSettings.AddAlternateKeyPaths)
	CreateAlternateKeyPath(path, entityType); //~/entitySet/{alternateKeyId}
	path.Push(new ODataKeySegment(entityType)); // ~/entitySet/{id}
	AppendPath(path.Clone());
	CreateTypeCastPaths(path, convertSettings, entityType, entitySet, false); // ~/entitySet/{id}/subType
	}

Will need to be resolved to fix: microsoftgraph/msgraph-metadata#427