I expect that there are many users with load on startup wallet definitions in `bitcoin.conf` or via startup CLI argument.
With the new `settings.json` r/w configuration file, users unloading and loading a wallet through the GUI or via the RPC calls might end up with a duplicate `-wallet` entry (one that still remains in `bitcoin.conf` or CLI) plus the new duplication in `settings.json` due to the unload/load.
Steps to reproduce
- create wallet (if via RPC set `load_on_startup` or unloadwallet/loadwallet then set `load_on_startup`).
- stop bitcoin
- start bitcoind again with same `--wallet=mywallet`
I guess it is acceptable to skip duplicates.
This is a backport of core#20199