Add support for non-default execution_count

[FredrikBakken]

Hi there 👋

First of all - we're using the nbstripout-fast as an alternative to nbstripout and absolutely love the performance increase in our pre-commit 🚀 However, we do have a suggestion for a supported feature.

Context

To give a bit of context, we have a team of Data Engineers where Databricks is our main compute engine for processing our notebooks. Some of the developers prefer to work locally with DatabricksConnect, while others prefer to use the Databricks UI. We're working on supporting both alternatives so that our developers can be in the environment they feel most efficient. The developers that use DatabricksConnect are actively using pre-commit, while Databricks does not support pre-commit directly so their lint-step inside our pipelines fails every time - and often times with nbstripout-fast.

Summary

Databricks will automatically set the execution_count value to 0, while nbstripout-fast sets it to null.

Our request is therefore that a new flag is added to the nbstripout-fast so that we can set a non-default execution_count value to our pre-commit. Could e.g. be something like: --default-execution-count <VALUE>