Allow merged idea links across portals

Related to https://big.ideas.aha.io/ideas/APP-I-6522.

If an idea is merged, the idea portal displays a link to the merged-to idea.

If an idea from one product is merged to an idea from a different product, and the products belong to different idea portals, the link is incorrect.

For example

• PRD1-I-1 is an idea for a product which is associated with an idea portal at https://portal1.ideas.aha.io

• PRD2-I-2 is an idea for a different product, which is associated with a different idea portal at https://portal2.ideas.aha.io/

• PRD1-I-1 was merged into PRD2-I-2.

• When a user goes to https://portal1.ideas.aha.io/ideas/PRD1-I-1, they see a banner stating that this idea is merged, with a link to PRD2-I-2.

• But the URL in the link is https://portal1.ideas.aha.io/ideas/PRD2-I-2 when it should be https://portal2.ideas.aha.io/ideas/PRD2-I-2.

Users see a link to the merged-to idea, but it is a broken link. We need to add a public comment to the idea.

Either give the correct link, or an option to not display a link.