Add path pointing to db migrations folder as opts for MapeoManager and MapeoProject

[achou11]

Description

Currently both MapeoManager and MapeoProject make assumptions about where the drizzle migration folders live:

https://github.com/digidem/mapeo-core-next/blob/110d6d8086c3d2e3cb052482420fa8f8256946db/src/mapeo-project.js#L87-L89

https://github.com/digidem/mapeo-core-next/blob/110d6d8086c3d2e3cb052482420fa8f8256946db/src/mapeo-manager.js#L68-L70

This generally is fine with our setup where where we publish the folders as part of the module, but becomes more problematic in cases where bundling is used (as we do on mobile app). To provide more flexibility, we should make these paths constructor opts that are specified for each class, that way the consumer can fully decide where these migration folders live in their application.

MapeoManager will require an opt for each db e.g. clientMigrationPath and projectMigrationPath while MapeoProject just needs one for the project db e.g. projectMigrationPath.

Tasks

• Add constructor opts for client migration and project migration folders for MapeoManager
• Add constructor opt for project migration folder for MapeoProject