feat: activate for "postgres" language ID

[aleclarson]

I have the following in my VSCode workspace settings:

"files.associations": {
  "*.sql": "postgres"
},

But this "breaks" the postgrestools extension.

As I understand it, the sqlfluff extension expects the "postgres" language ID since I have dialect = postgres in my sqlfluff config.

[juleswritescode]

Nice! Thank you very much :)