Elektra: Global Validation

Elektra 0.8.24

Global Validation

## Problem

Links and validation constraints might point to keys not loaded with the respective `kdbGet`.

## Constraints

- no workaround such as `kdb get -a`

## Assumptions

## Considered Alternatives

- global plugin can register additional backends to load
- split `kdbGet` into multiple steps: 0. do `kdbGet` on `system/elektra` to update mountpoints
  1. first do `kdbGet` on the `spec/`-namespace
  2. then calculate which backends are needed
  3. then fetch all backends as needed
- split loops in `kdbGet` not only according placements but also according namespace (get spec first)

## Decision

## Rationale

## Implications

## Related decisions

## Notes

see #1291