Data source extensions should be composable (see text)

[Apollo3zehn]

The following parts of an extension are often subject to customizations:

• custom renaming rules for channels (e.g. to make them shorter, translate strange names or make names Nexus compliant)
• flexible selection of group names (do not use dataSourceId for this anymore)
• files are not always located in a regular file system, sometimes they are elsewhere (e.g. OneDrive), so we need a way to exchange the underlying file transport
• file search algorithms: the default one of the "StructuredFileSource" assumes files to be present in a structured way (regular timestamps, ...). This is not always the case and sometimes a custom algorithm would be useful (this is already possible by overwriting a specific method)
• group multiple data sources into a single catalog: maybe this becomes possible with separate file source groups (via StructuredDataSource) or a similar feature applicable to all types of data sources?