[APM] Deprecate obsolete `xpack.apm.serviceMapEnabled` config options

[sorenlouv]

The settings xpack.apm.serviceMapEnabled should be removed since there's no longer any reason to disable the service map

[smith]

You can provide deprecations and rename keys, even moving them to advanced settings. Example here:

kibana/src/core/server/ui_settings/ui_settings_config.ts

Line 15 in 4584a8b

renameFromRoot('server.defaultRoute', 'uiSettings.overrides.defaultRoute'),