Add detailed recommendations for filenames of archetypes and templates

There should be recommendations for filenames of archetypes and templates. The rationale of providing recommendations for this in the specifications is to ensure uniqueness and consistency: Uniqueness is required to ensure that similar long names are always mapped to a unique short name. Consistency is valuable so that various tooling may be able to pick up the correct file from - say - the archetype id or template name. This should take into account the following aspects: 1. Maximum filename length. Different OS have different limitations, linux-based system usually have a maximum of 255 characters / bytes, whereas Windows systems (without the long path option enabled) typically support 260 characters for the complete Path. 2. Shortening of filenames exceeding the maximum length Initial Ideas from various SEC members: - Could truncate appropriately and append the GUID - long → short name-mapping, provided in a separate text file - work with shortening of common parts of the archetype id and URL-encoding, could also be hashed 3. Replacement of characters with unclear support across operating systems/file systems. For example \ / : < > | * ? " may not be safe for use. See https://openehr.atlassian.net/wiki/spaces/spec/pages/1983479809/2022-04-04+SEC+Call+notes for further details on the initial discussion