Add phpcs rule to ensure one line is left empty after function declaration

Currently PHPCS does not flag this as warning(which it should) -
```
function abc($a) {
if($a){
...
}
}
```

This is the coding the team has agreed to(and it should not display warning) -
```
function abc($a) {

if($a){
...
}
}
```

`phpcs.xml` needs to be modified in this and all the commands and site type repos.