PoC for multitenancy support

[Enforcer]

Play around with API.

The first attempt assumes using ContextVars and context managers:

from event_sourcery.event_store.context import event_sourcery_context

with event_sourcery_context(tenant_id=1):
    # do sth as tenant_1, e.g. create streams etc

There are lots of open questions, e.g.

• how far the isolation should go,
• is it possible to achieve certain things stuff in EventStoreDB etc
• should we allow the same stream IDs inside the tenant context as well as outside of it (and should tenants be able to reuse the same stream_id),
• the same goes for stream names
• should we rather have a separate EventStore subclass that allows to work with multitenancy and by default have this disabled (so it looks like there is no multitenancy)

Here's some Example Mapping I tried to make to visualize how I think about it: