Ability to modify wal and configs path in InfluxDB v2.x config.

__Proposal:__
Ability to modify wal and configs path via influxdb config file.

__Current behavior:__
The option to set wal path is missing after migrating from 1.8 to 2.x. The configs directory is new, but no option to set where to be stored.

__Desired behavior:__
Option in the config where we can define where these paths should be stored.

__Alternatives considered:__
N/A

__Use case:__
I want to maintain engine and wal on 2 different disks in order to gather more performance when writing metrics to InfluxDB.
In the old versions, we had the option to use wal-dir parameter and use secondary mount point for writing Write Ahead Log.
In this case I can choose a small size but high I/O disk for wal and a large but standard nvme for engine/data storage.

InfluxDB v2.6.1 Server: [9dcf880](https://github.com/influxdata/influxdb/tree/9dcf880fe0)
Frontend: [5ba8e15](https://github.com/influxdata/ui/tree/5ba8e15)

Thank you.

Start with the InfluxDB v2.x config-file handling and the existing engine and WAL path settings. Determine how configuration defines storage locations and what must change to support separate configurable WAL and configs paths. Done means both paths can be set in the config while engine and WAL storage remain independently placeable.

Written by the indexing model from the issue text.