Check the OCI container format for deployment configuration

[ueno]

As described in the wiki, we are going to split our configuration file into two parts: build time and deployment time. Currently we have a single configuration file that is bundled in the Wasm binary itself, though an OCI-based package format has been proposed for similar purposes:

• https://www.solo.io/blog/announcing-the-webassembly-wasm-oci-image-spec/
• https://radu-matei.com/blog/wasm-to-oci/

This issue is to check whether the OCI package format meets our needs. #22 probably depends on this.

[ueno]

I tried the proposed tooling on those blogs. It cannot be simply compared with the current bundling format (on disk), because the OCI format rather defines a way to resolve contents on the registry. However, as it allows the data to be addressed by content, it could be beneficial if keepmgr provides caching and the same Wasm files are reused with different configurations.