Add immutable option to make the tenantId field immutable

[IvoFritsch]

Mongoose has the property immutable for a field. It would be cool to add this option in the plugin.

for example: SomeSchema.plugin(mongoTenant, { ... , immutable: true });

Thanks in advance

[alrik]

I like this.

For further reference: https://mongoosejs.com/docs/api/schematype.html#schematype_SchemaType-immutable