Support for URNs and colon containing ids

[alexander-schranz]

Using URNs (Uniform Resource Name) are a way to store identifiers of models / documents.

Currently meilisearch fails using URNs as primary key with

A document identifier can be of type integer or string, only composed of alphanumeric characters (a-z A-Z 0-9), hyphens (-) and underscores (_), and can not be more than 511 bytes.

I think it would be a great feature to also support the colon (:) inside primary keys to support URN or URN like identifiers.

More about URNs:

• https://learn.microsoft.com/de-de/linkedin/shared/api-guide/concepts/urns
• https://www.ietf.org/rfc/rfc2141.txt
• https://en.wikipedia.org/wiki/Uniform_Resource_Name