source-shopify-native: Make bulk query concurrency limit configurable

[SeanWhelan]

The connector currently hardcodes MAX_CONCURRENT_BULK_OPS = 5 in bulk_job_manager.py and uses all 5 slots Shopify allows. Customers who have other systems submitting bulk queries to the same store have no way to reserve slots for those systems.

Proposed change:
Add a max_concurrent_bulk_ops field to the Endpoint Config -> Advanced section (1, 5) and pass it through to the connector.

[Alex-Bair]

Whenever it starts up, the connector also attempts to cancel all currently running bulk query jobs. Right now, that's fine since we're assuming the connector is the only application making bulk queries & can utilize all 5 bulk query slots. But once the connector's no longer the only app submitting bulk queries, it shouldn't blindly cancel all running bulk queries. It'll need a way to identify which bulk jobs it previously submitted & only cancel those.

One way to do this is by adding an identifying comment into the GraphQL query, like # Estuary Flow Managed Bulk Query, and only cancel jobs where that specific string shows up in the query field.