feat(registry): add registry proxy plugin

[pinglin]

Because

• Instill Artifact is going to have a OCI-compatible artifact registry service!

This commit

• implement a KrakenD plugin for the registry proxy

[linear]

INS-3906 implement the corresponding api-gateway routing to the remote docker registry

[jvallesm]

Thanks for taking care of this! 💪

❓ I have some questions to make sure I'm understanding the design.

• How will the configuration look like to point to the model registry?
• And when we have model and pipeline registries?
• Do you have some sort of end-to-end diagram illustrating what we're trying to achieve with this plugin? It will be helpful to make sure we're aligned on the design.

[pinglin]

• How will the configuration look like to point to the model registry?

It should be as simple as specifying the registry network address by setting the corresponding api-gateway environment variables.

• And when we have model and pipeline registries?

We are going to have model registry first. This is crucial to support the new model containerisation design which @heiruwu and @tonywang10101 are working on.

• Do you have some sort of end-to-end diagram illustrating what we're trying to achieve with this plugin? It will be helpful to make sure we're aligned on the design.

A very high-level architecture looks like this:

[jvallesm]

Sorry for the late review, didn't find time yesterday.

I added some comments, only one requires actual discussion (the username variable not being set).