[Bug] Marquez fails due to empty namespace name

[YLibert]

Issue

Marquez fails to load when a Namespace with an empty name is in its database

Root cause

We received an event coming from the Airflow Integration:

{
  "job": {
    "name": "hello_world.create_table",
    "facets": {
      "sql": {
        "query": "REDACTED",
        "_producer": "https://github.com/OpenLineage/OpenLineage/tree/0.21.1/integration/airflow",
        "_schemaURL": "https://raw.githubusercontent.com/OpenLineage/OpenLineage/main/spec/OpenLineage.json#/definitions/SqlJobFacet"
      },
      "ownership": {
        "owners": [
          {
            "name": "airflow"
          }
        ],
        "_producer": "https://github.com/OpenLineage/OpenLineage/tree/0.21.1/integration/airflow",
        "_schemaURL": "https://raw.githubusercontent.com/OpenLineage/OpenLineage/main/spec/OpenLineage.json#/definitions/OwnershipJobFacet"
      },
      "documentation": {
        "_producer": "https://github.com/OpenLineage/OpenLineage/tree/0.21.1/integration/airflow",
        "_schemaURL": "https://raw.githubusercontent.com/OpenLineage/OpenLineage/main/spec/OpenLineage.json#/definitions/DocumentationJobFacet",
        "description": "Hello world example"
      }
    },
    "namespace": "REDACTED"
  },
  "run": {
    "runId": "619939e3-d8bf-38e2-b4f5-3285f4f10f03",
    "facets": { ... Lenghty Airflow facets not relevant here...}
  },
  "inputs": [],
  "outputs": [
    {
      "name": "REDACTED",
      "facets": {
        "dataSource": {
          "uri": "REDACTED",
          "name": "",
          "_producer": "https://github.com/OpenLineage/OpenLineage/tree/0.21.1/integration/airflow",
          "_schemaURL": "https://raw.githubusercontent.com/OpenLineage/OpenLineage/main/spec/OpenLineage.json#/definitions/DataSourceDatasetFacet"
        }
      },
      "namespace": ""
    }
  ],
  "producer": "https://github.com/OpenLineage/OpenLineage/tree/0.21.1/integration/airflow",
  "eventTime": "2023-07-19T14:45:44.487112Z",
  "eventType": "START"
}

I redacted some of the info as it is from a preproduction env.

This resulted in the creation of a namespace of name '' in the database.

As a result, the Marquez main page could not load due to an error 500:

! java.lang.IllegalArgumentException: namespace '' must contain only letters (a-z, A-Z), numbers (0-9), underscores (_), at (@), plus (+), dashes (-), colons (:), equals (=), semicolons (;), slashes (/) or dots (.) with a maximum length of 1024 characters.