fix(postgresql_lsp): update command to use lsp-proxy argument (#3636)

Problem:
The current command "postgresql_lsp" doesn't work as expected because
the server requires the "lsp-proxy" argument to function properly.

Solution:
Update the cmd to use ("postgresql_lsp", "lsp-proxy") to correctly
invoke the language server with its required arguments.

lua/lspconfig/configs/postgres_lsp.lua

@@ -2,7 +2,7 @@ local util = require 'lspconfig.util'
 
 return {
   default_config = {
-    cmd = { 'postgres_lsp' },
+    cmd = { 'postgres_lsp', 'lsp-proxy' },
     filetypes = { 'sql' },
     root_dir = util.root_pattern 'root-file.txt',
     single_file_support = true,