[fmt]: Allow disabling trailing commas

[sakgoyal]

Would you consider adding an option to disable trailing commas in the fmt config in deno.json? I am trying to migrate a large project to deno from node, but without this, it makes a really big diff in git.

I want to keep the change minimal for the project, but this changes thousands of lines.

Suggested implementation

// deno.jsonc 
"fmt" : {
    // ...
    "trailingCommas" : false
}