Merge branch 'axil-add-external-url-variable' into 'master'

Add EXTERNAL_URL to the list of environment variables

See merge request gitlab-org/gitlab!71358

doc/administration/environment_variables.md

@@ -21,6 +21,7 @@ You can use the following environment variables to override certain values:
 |--------------------------------------------|---------|---------------------------------------------------------------------------------------------------------|
 | `DATABASE_URL`                             | string  | The database URL; is of the form: `postgresql://localhost/blog_development`.                            |
 | `ENABLE_BOOTSNAP`                          | string  | Enables Bootsnap for speeding up initial Rails boot (`1` to enable).                                    |
+| `EXTERNAL_URL`                             | string  | Specify the external URL at the [time of installation](https://docs.gitlab.com/omnibus/settings/configuration.html#specifying-the-external-url-at-the-time-of-installation). |
 | `EXTERNAL_VALIDATION_SERVICE_TIMEOUT`      | integer | Timeout, in seconds, for an [external CI/CD pipeline validation service](external_pipeline_validation.md). Default is `5`. |
 | `EXTERNAL_VALIDATION_SERVICE_URL`          | string  | URL to an [external CI/CD pipeline validation service](external_pipeline_validation.md).                |
 | `EXTERNAL_VALIDATION_SERVICE_TOKEN`        | string  | The `X-Gitlab-Token` for authentication with an [external CI/CD pipeline validation service](external_pipeline_validation.md). |