Add support for multiple bicep modules

Today we added support for a single bicep file via a string, embedded resource or a file. There are some situations where multiple modules are needed (usually because of ARM or bicep limitations). We should extend the bicep resource to support a single main file (what we have today) and multiple modules that are stored either as resources or files on disk. When the manifest is published, we should copy all of the files to a subfolder and move all modules relative to the main bicep file. We may need to represent the modules as well.

Start by tracing the existing single-file Bicep resource and the manifest publication path. Determine how resources or files are represented and how module paths are resolved relative to the main file. Done means a main Bicep file can publish with multiple resource- or disk-backed modules copied into a subfolder with working relative references.

Written by the indexing model from the issue text.