Add modelserving architecture doc

[Jooho]

Description

This PR contains documentation aimed at explaining the architecture of the component managed by the modelserving team. Essentially, it provides a high-level overview of what each component does.

How Has This Been Tested?

No source changed.

Merge criteria:

• [ ] The commits are squashed in a cohesive manner and have meaningful messages.
• [ ] Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• [ ] The developer has manually tested the changes and verified that the changes work

[danielezonca]

@Jooho Please include the source (drawio format is ideal) of the diagram too to simplify the changes in the future