Documentation: Add backend module ownership map and maintainers table

[Junirezz]

Document backend modules and ownership to improve triage and review routing.

[afeezorobsco-cyber]

@afeezorobsco-cyber has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

hi maintainer, can i work on this issue?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @afeezorobsco-cyber to this issue.