Move config parameters to init paramters

[lukecyca]

Is your feature request related to a problem? Please describe.

The only way to configure this library is through Kconfig parameters. This is inconvenient if the application code needs to choose these parameters at runtime. This most obvious example is setting the SSID to something device-specific, which is important it there are multiple devices requiring provisioning.

Describe the solution you'd like
I would like DEFAULT_AP_SSID, DEFAULT_HOSTNAME, and possibly some others removed from Kconfig and passed to wifi_manager_start().

Describe alternatives you've considered
I could edit wifi_manager.h, but that still doesn't allow setting these names dynamically with device-specific identifiers. I could edit the library and maintain a fork, but I prefer to fix this upstream.