[MRESOLVER-163] Introduce "configuration" or "feature" helper to centralize various flags/params/configs

**[Tamas Cservenak](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=cstamas)** opened **[MRESOLVER-163](https://issues.apache.org/jira/browse/MRESOLVER-163?redirect=false)** and commented

Currently we have all kind of `aether...` keyed properties (see https://maven.apache.org/resolver/configuration.html) available to configure Maven Resolver behaviour.
Bad1: they are spread across codebase
Bad2: it is not always clear, is it sourced from session or system property or both

So, I'd propose to MOVE all these keys (and probably their handling (reading) code into here as well, so we could have
Good1: all these keys would be listed at one place (easier to document, check, etc)
Good2: simply, one class introspection (reading by dev) would tell all the story of it.

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**Issue Links:**
- [MRESOLVER-310](https://issues.apache.org/jira/browse/MRESOLVER-310) Preserve configuration of Enhanced LRM in local repo

Start with the Maven Resolver configuration documentation and search the codebase for the existing aether-keyed properties and their session or system-property handling. Inventory those keys and sources, then define the centralized configuration or feature helper and update the related documentation so one class exposes the complete configuration story.

Written by the indexing model from the issue text.