Workers Templates serde and schema evolution support

[vigoo]

• fix TemplateMetadata serde - we have TODO in case of FunctionResult.typ and FunctionParameter.typ - where in relation to naming fixes, original tpe was renamed to typ ; as there was issue to read stored data, we added #[serde(rename = "tpe")] for those attributes, (should not we consider to add custom structure-s, with custom serde, to decouple internal storage implementation and API implementation?)
• add support for versioning of metadata in TemplateRepo

[vigoo]

Closed in favor of #498