[target/windows] Fix KBN_PATH_CONF expansion in bin/*.bat (#104517)

When setting the environment variable KBN_PATH_CONF in Windows, paths
containing special characters will be expanded and interpreted, instead
of being treated as a string.  This wraps `%KBN_PATH_CONF%` in quotes to
prevent this.

Testing:
1) set "KBN_PATH_CONF=C:\With space\special()%$characters\kibana\config"
2) bin\kibana*.bat should run

src/dev/build/tasks/bin/scripts/kibana-encryption-keys.bat

@@ -13,7 +13,7 @@ If Not Exist "%NODE%" (
 )
 
 set CONFIG_DIR=%KBN_PATH_CONF%
-If [%KBN_PATH_CONF%] == [] (
+If ["%KBN_PATH_CONF%"] == [] (
   set "CONFIG_DIR=%DIR%\config"
 )
 

src/dev/build/tasks/bin/scripts/kibana-keystore.bat

@@ -13,7 +13,7 @@ If Not Exist "%NODE%" (
 )
 
 set CONFIG_DIR=%KBN_PATH_CONF%
-If [%KBN_PATH_CONF%] == [] (
+If ["%KBN_PATH_CONF%"] == [] (
   set "CONFIG_DIR=%DIR%\config"
 )
 

src/dev/build/tasks/bin/scripts/kibana-plugin.bat

@@ -14,7 +14,7 @@ If Not Exist "%NODE%" (
 )
 
 set CONFIG_DIR=%KBN_PATH_CONF%
-If [%KBN_PATH_CONF%] == [] (
+If ["%KBN_PATH_CONF%"] == [] (
   set "CONFIG_DIR=%DIR%\config"
 )
 

src/dev/build/tasks/bin/scripts/kibana.bat

@@ -15,7 +15,7 @@ If Not Exist "%NODE%" (
 )
 
 set CONFIG_DIR=%KBN_PATH_CONF%
-If [%KBN_PATH_CONF%] == [] (
+If ["%KBN_PATH_CONF%"] == [] (
   set "CONFIG_DIR=%DIR%\config"
 )