Re-enable @typescript-eslint/no-namespace when better option for globalThis module augmentation available

[karlhorky]

We disabled @typescript-eslint/no-namespace in 2e1673d to avoid the ES2015 module syntax is preferred over namespaces. eslint (@typescript-eslint/no-namespace) error with the following globalThis module augmentation code:

declare module globalThis {
  let postgresSqlClient: Sql;
}

Once there is a better option available, we should re-enable @typescript-eslint/no-namespace

• Docs: globalThis without ignores of no-var and no-namespace typescript-eslint/typescript-eslint#9582
• Base rule extension: no-var configuration for declarations typescript-eslint/typescript-eslint#7941
• [no-var] var & Type-checking for globalThis typescript-eslint/typescript-eslint#3617