docs: Connector Builder contribution flow text-based docs (#44616)

docs/connector-development/cdk-python/migration-to-base-image.md

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+# Migration Guide: How to make a python connector use our base image
+
+We currently enforce our certified python connectors to use our [base image](https://hub.docker.com/r/airbyte/python-connector-base).
+This guide will help connector developers to migrate their connector to use our base image.
+
+N.B: This guide currently only applies to Python CDK connectors.
+
+## Prerequisite
+
+[Install the airbyte-ci tool](https://github.com/airbytehq/airbyte/blob/master/airbyte-ci/connectors/pipelines/README.md#L1)
+
+## Definition of a successful migration
+
+1. The connector `Dockerfile` is removed from the connector folder
+2. The connector `metadata.yaml` is referencing the latest base image in the `data.connectorBuildOptions.baseImage` key
+3. The connector version is bumped by a patch increment
+4. A changelog entry is added to the connector documentation file
+5. The connector is successfully built and tested by our CI
+6. If you add `build_customization.py` to your connector, the Connector Operations team has reviewed and approved your changes.
+
+## Semi automated migration
+
+- Run `airbyte-ci connectors --name=<my-connector> migrate_to_base_image <PR_NUMBER>`
+- Commit and push the changes on your PR
+
+## Manual migration
+
+In order for a connector to use our base image it has to declare it in its `metadata.yaml` file under the `data.connectorBuildOptions.baseImage` key:
+
+Example:
+
+```yaml
+connectorBuildOptions:
+  baseImage: docker.io/airbyte/python-connector-base:1.1.0@sha256:bd98f6505c6764b1b5f99d3aedc23dfc9e9af631a62533f60eb32b1d3dbab20c
+```
+
+### Why are we using long addresses instead of tags?
+
+**For build reproducibility!**.
+Using full image address allows us to have a more deterministic build process.
+If we used tags our connector could get built with a different base image if the tag was overwritten.
+In other word, using the image digest (sha256), we have the guarantee that a build, on the same commit, will always use the same base image.
+
+### What if my connector needs specific system dependencies?
+
+Declaring the base image in the metadata.yaml file makes the Dockerfile obselete and the connector will be built using our internal build process declared [here](https://github.com/airbytehq/airbyte/blob/master/airbyte-ci/connectors/pipelines/pipelines/airbyte_ci/connectors/build_image/steps/python_connectors.py#L55).
+If your connector has specific system dependencies, or has to set environment variables, we have a pre/post build hook framework for that.
+
+You can customize our build process by adding a `build_customization.py` module to your connector.
+This module should contain a `pre_connector_install` and `post_connector_install` async function that will mutate the base image and the connector container respectively.
+It will be imported at runtime by our build process and the functions will be called if they exist.
+
+Here is an example of a `build_customization.py` module:
+
+```python
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    # Feel free to check the dagger documentation for more information on the Container object and its methods.
+    # https://dagger-io.readthedocs.io/en/sdk-python-v0.6.4/
+    from dagger import Container
+
+
+async def pre_connector_install(base_image_container: Container) -> Container:
+    return await base_image_container.with_env_variable("MY_PRE_BUILD_ENV_VAR", "my_pre_build_env_var_value")
+
+async def post_connector_install(connector_container: Container) -> Container:
+    return await connector_container.with_env_variable("MY_POST_BUILD_ENV_VAR", "my_post_build_env_var_value")
+```
+
+### Listing migrated / non migrated connectors:
+
+To list all migrated certified connectors you can ran:
+
+```bash
+airbyte-ci connectors --support-level=certified --metadata-query="data.connectorBuildOptions.baseImage is not None" list
+```
+
+To list all non migrated certified connectors you can ran:
+
+```bash
+airbyte-ci connectors --metadata-query="data.supportLevel == 'certified' and 'connectorBuildOptions' not in data.keys()" list
+```