[Persistence/Projections] Reorganize reference docs

[ignasi35]

The ref docs in https://doc.akka.io/docs/akka/current/typed/index-persistence.html don't expose akka-projections unless you go searching for the project under Other Akka modules.

At the same time, the Persistence section in the docs does introduce queries and writing plugins and other advanced topics the general user is unlikely to care about.

• Current structure

    Security Announcements
    Getting Started Guide
    General Concepts
    Actors
    Cluster
    Persistence
        Event Sourcing
        Replicated Event Sourcing
        CQRS
        Style Guide
        Snapshotting
        Testing
        EventSourced behaviors as finite state machines
        Schema Evolution for Event Sourced Actors
        Persistence Query
        Persistence Query for LevelDB
        Persistence Plugins
        Persistence - Building a storage backend
        Replicated Event Sourcing Examples
    Streams
    Discovery
    Utilities
    Other Akka modules
    Package, Deploy and Run
    Project Information
    Akka Classic

• Suggested structure

    Security Announcements
    Getting Started Guide
    General Concepts
    Actors
    Cluster
    Persistence
        Event Sourcing
        Replicated Event Sourcing
        CQRS
        Style Guide
        Snapshotting
        Testing
        EventSourced behaviors as finite state machines
        Schema Evolution for Event Sourced Actors
        Projections (add a page to promote projections, could be a link to the CQRS page above)
        Persistence Query
        Advanced topics (hide all other sections under here)
    Streams
    Discovery
    Utilities
    Other Akka modules
    Package, Deploy and Run
    Project Information
    Akka Classic

[octonato]

I agree that the more advanced topics should get it's own section.

About the Projections page, it's so much related to Persistence Query, that we could instead rename the latter to "Persistence Query and Projections" and have projections as a subsection under the Query page.

I think the ordering is also important. First we explain how to query, then we explain that you can use eventsByTag with Akka Projections.

[johanandren]

One thing to remember if we re-organize the structure is that we need to keep redirects from the old structure paths, to not break links into the docs from external places.

[ignasi35]

One thing to remember if we re-organize the structure is that we need to keep redirects from the old structure paths, to not break links into the docs from external places.

Good point.

Would it be possible to change the left-most menu without altering the URLs? I think that would be ideal.

In this issue, I'm only concerned about the navigation and relevance/discoverability each section has.

[johanandren]

I think the navigation menu is entirely dictated by the various @index ... listings in the different levels of index.md-files, while the title in the menu comes from the l1 header in the files, separate from the actual file names and directory structure.