[Feature Request]: External tag stores

[TrigamDev]

Checklist

• I am using an up-to-date version.
• I have read the documentation.
• I have searched existing issues.

Description

This would be similar to global tags (#680) that are currently planned, but it would be really convenient to be able to create multiple external tag stores that can be used by different libraries. That way, you could create separate stores for similar tags, and then only use the stores that are relevant to a library, rather than every tag being global and having a ton of irrelevant tags clogging up the tag manager.

In my use case, it would be really nice to separate some of my tags into their own databases, such as color tags, meta tags, shot/composition tags, etc. This would be made much more useful once component tags are implemented. For example, I could then use the base color tags database to compose color variations of other tags.

Solution

• Allow for the creation of separate tag databases, which will only store tag-related information.
• A new table should be added to libraries (similar to the folders table), where each tag database a library is using will be tracked with a path and ID. This should also be present in tag databases, in the case that a tag is a child of one from another database.
• In any place where a tag ID is used, an extra field should be added also tracking which tag database ID it belongs to.
• A tool should be added to easily move a tag to and from different databases.

Alternatives

Currently, the only solution is to just duplicate all the tags you would like to use between different libraries.