Add new dependency scanning var for specifying the pip version

changelogs/unreleased/12811-add-pip-version-dep-scanning-flag.yml

+---
+title: Add CI variable to set the version of pip when scanning dependencies of Python projects
+merge_request: 21218
+author:
+type: added

doc/user/application_security/dependency_scanning/index.md

@@ -134,6 +134,7 @@ using environment variables.
 | `DS_ANALYZER_IMAGE_PREFIX`              | Override the name of the Docker registry providing the official default images (proxy). Read more about [customizing analyzers](analyzers.md). |
 | `DS_ANALYZER_IMAGE_TAG`                 | Override the Docker tag of the official default images. Read more about [customizing analyzers](analyzers.md). |
 | `DS_PYTHON_VERSION`                     | Version of Python. If set to 2, dependencies are installed using Python 2.7 instead of Python 3.6. ([Introduced](https://gitlab.com/gitlab-org/gitlab/issues/12296) in GitLab 12.1)|
+| `DS_PIP_VERSION`                        | Force the install of a specific pip version (example: `"19.3"`), otherwise the pip installed in the docker image is used. |
 | `DS_PIP_DEPENDENCY_PATH`                | Path to load Python pip dependencies from. ([Introduced](https://gitlab.com/gitlab-org/gitlab/issues/12412) in GitLab 12.2) |
 | `DS_DEFAULT_ANALYZERS`                  | Override the names of the official default images. Read more about [customizing analyzers](analyzers.md). |
 | `DS_DISABLE_DIND`                       | Disable Docker in Docker and run analyzers [individually](#disabling-docker-in-docker-for-dependency-scanning).|

lib/gitlab/ci/templates/Security/Dependency-Scanning.gitlab-ci.yml

@@ -47,6 +47,7 @@ dependency_scanning:
           DS_PULL_ANALYZER_IMAGE_TIMEOUT \
           DS_RUN_ANALYZER_TIMEOUT \
           DS_PYTHON_VERSION \
+          DS_PIP_VERSION \
           DS_PIP_DEPENDENCY_PATH \
           PIP_INDEX_URL \
           PIP_EXTRA_INDEX_URL \