meson: add dependency for nlohmann-json

nlohmann-json is not always installed, especially when developers are
attempting to do out-of-Docker builds.  Meson subprojects are the
method we use to handle this case.  Add the meson subproject wrap and
appropriate dependency values in the meson.build files.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Id855f8e320d9ab9332a3803f6ab0dff3aebfd39b
diff --git a/meson.build b/meson.build
index 5611661..2b63b33 100644
--- a/meson.build
+++ b/meson.build
@@ -83,6 +83,7 @@
 
 boost_dep = dependency('boost')
 ldap_dep = cpp.find_library('ldap', required: false)
+nlohmann_json_dep = dependency('nlohmann_json', include_type: 'system')
 pam_dep = dependency('pam')
 phosphor_dbus_interfaces_dep = dependency('phosphor-dbus-interfaces')
 phosphor_logging_dep = dependency('phosphor-logging')
@@ -115,10 +116,11 @@
 
 user_manager_deps = [
     boost_dep,
+    nlohmann_json_dep,
     pam_dep,
-    sdbusplus_dep,
-    phosphor_logging_dep,
     phosphor_dbus_interfaces_dep,
+    phosphor_logging_dep,
+    sdbusplus_dep,
 ]
 
 user_manager_lib = static_library(
diff --git a/subprojects/nlohmann_json.wrap b/subprojects/nlohmann_json.wrap
new file mode 100644
index 0000000..3745380
--- /dev/null
+++ b/subprojects/nlohmann_json.wrap
@@ -0,0 +1,6 @@
+[wrap-git]
+revision = HEAD
+url = https://github.com/nlohmann/json.git
+
+[provide]
+nlohmann_json = nlohmann_json_dep