Boost: Refactor Image CDN features into sub modules

[dilirity]

Proposed changes:

• Move Image CDN features (Liar and Quality Settings) to sub modules;
• Add sub modules to Jetpack sync.

Other information:

• [ ] Have you written new tests for your changes, if applicable?
• [ ] Have you checked the E2E test CI results, and verified that your changes do not break them?
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Jetpack product discussion

n/a

Does this pull request change what data or activity we track or use?

no

Testing instructions:

• Setup Boost premium and make sure LIAR and the Quality Settings work as expected.

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[dilirity]

After a call with @pyronaur, I'm going to do some refactoring. Reverted this to draft.

[pyronaur]

Great to see that you noticed that the Submodule looks very similar to a Module! 👍

To summarize what we talked about on the call - instead of creating a new thing called "Submodule" - what if we consider that they're all Modules anyway? We can have a special interface that marks that the Module has children (something like Has_Children or Has_Submodules) and then when setup is called, look for that interface, and if it's true - recursively call the init on each of the children too.

And to return the data, since we only need that for debug purposes anyway - create another interface called Has_Debug and use that to check if there's additional debug information that needs to be added as well.