Configuration behavior docs

### Is there an existing issue for this?

- [x] I have searched the existing issues

### What's missing?

Configuration should have behavior docs that explain how remote configs are downloaded, including some hidden behavior like the 15 sec minimum redownload window:
https://github.com/adobe/aepsdk-core-ios/blob/c3727f6b2a25a8e395ee71d42d1671e12851db84/AEPCore/Sources/configuration/Configuration.swift#L135-L138

Start with Configuration.swift at the linked lines to verify how remote configurations are downloaded and how the 15-second minimum redownload window works. Add behavior documentation covering these details, with completion indicated by the remote configuration download and redownload rules being clearly explained.

Written by the indexing model from the issue text.