2022-10-01 WireGuard volumes restructure - master branch - PR 1 of 3

[Paraphraser]

WireGuard has started renaming the custom-services.d and custom-cont-init.d directories to have random suffixes, along with the following README.txt:

********************************************************
********************************************************
*                                                      *
*                         !!!!                         *
* Custom scripts or services found in legacy locations *
*                         !!!!                         *
*    Please move your custom scripts and services      *
*    to /custom-cont-init.d and /custom-services.d     *
*    respectively to ensure they continue working.     *
*                                                      *
*  Visit https://linuxserver.io/custom for more info.  *
*                                                      *
********************************************************
********************************************************

Some existing installations have also failed. Remote clients are unable to connect with docker logs wireguard cycling the following messages:

s6-supervise custom-svc-README.txt (child): fatal: unable to exec run: Exec format error
s6-supervise custom-svc-README.txt: warning: unable to spawn ./run - waiting 10 seconds

The container does not go into a restart loop so docker ps does not alert the user to the situation.

This PR:

1. implements the required changes to the WireGuard service definition;
2. provides a script to assist with the necessary folder restructuring;
3. adds a section to the IOTstack WireGuard documentation (master branch) to explain the process.

Signed-off-by: Phill Kelley 34226495+Paraphraser@users.noreply.github.com