Add an automatic error message printed to UART emphasising the fact that
CONFIG_NRF_CLOUD_PROVISION_CERTIFICATES is inherently insecure and
should only be used for testing purposes.

Also mark NRF_CLOUD_PROVISION_CERTIFICATES as experimental.

Signed-off-by: Georges Oates_Larsen <georges.larsen@nordicsemi.no>

Slightly modify CMakeLists.txt to automatically search for secrets in
local certs directory if CONFIG_NRF_CLOUD_PROVISION_CERTIFICATES is
enabled.

Also add .gitignore entry to prevent said certs folder from ever being
accidentally committed.

Signed-off-by: Georges Oates_Larsen <georges.larsen@nordicsemi.no>

When CONFIG_DATE_TIME_AUTO_UPDATE is disabled, manually trigger
date_time timestamp update whenever network connection is achieved

Signed-off-by: Georges Oates_Larsen <georges.larsen@nordicsemi.no>

If NRF_CLOUD_EVT_TRANSPORT_CONNECT_ERROR is raised by nrf_cloud,
reset connection and retry immediately rather than wait for the
readiness timeout.

Signed-off-by: Georges Oates_Larsen <georges.larsen@nordicsemi.no>

Adds overlay to use Wi-Fi conn_mgr layer instead of LTE conn_mgr layer.
Also removes a couple remaining dependencies on the nrf9160 modem.

IRIS-4800

Signed-off-by: Georges Oates_Larsen <georges.larsen@nordicsemi.no>

Add docs explaining how to build and provision for Wi-Fi connectivity.

Signed-off-by: Georges Oates_Larsen <georges.larsen@nordicsemi.no>