docs: normalise table headers

It is bound to the `test` stage, and uses the following variables:

| Name                     | description                     | default value |

| Name                     | Description                     | Default value |

| ------------------------ | ------------------------------- | ----------------------------- |

| `SONAR_SCANNER_IMAGE`    | The Docker image used to run [sonar-scanner](https://docs.sonarqube.org/latest/analysis/scan/sonarscanner/) | `registry.hub.docker.com/sonarsource/sonar-scanner-cli:latest` |

| `SONAR_HOST_URL`         | SonarQube server url            | _none_ (disabled) |

In order to be able to communicate with the Vault server, the variant requires the additional configuration parameters:

| Name              | description                            | default value     |

| Name              | Description                            | Default value     |

| ----------------- | -------------------------------------- | ----------------- |

| `TBC_VAULT_IMAGE` | The [Vault Secrets Provider](https://gitlab.com/to-be-continuous/tools/vault-secrets-provider) image to use (can be overridden) | `$CI_REGISTRY/to-be-continuous/tools/vault-secrets-provider:master` |

| `VAULT_BASE_URL`  | The Vault server base API url          | _none_ |

With:

| Name                             | description                            |

| Name                             | Description                            |

| -------------------------------- | -------------------------------------- |

| `secret_path` (_path parameter_) | this is your secret location in the Vault server |

| `field` (_query parameter_)      | parameter to access a single basic field from the secret JSON payload |