chore: Update discovery artifacts (#1374)

## Discovery Artifact Change Summary:
feat(gkehub): update the api https://github.com/googleapis/google-api-python-client/commit/b2c1bb00a3b41e9cdfe925dd90aa4bc677a55e33
feat(servicedirectory): update the api https://github.com/googleapis/google-api-python-client/commit/1a87cd4c32ff6145efb48dcbf12e644da1533f0b
feat(servicenetworking): update the api https://github.com/googleapis/google-api-python-client/commit/12d70c78040997c7354bcf66a0afe6b428d493d6
diff --git a/googleapiclient/discovery_cache/documents/retail.v2beta.json b/googleapiclient/discovery_cache/documents/retail.v2beta.json
index e963b91..fcdc113 100644
--- a/googleapiclient/discovery_cache/documents/retail.v2beta.json
+++ b/googleapiclient/discovery_cache/documents/retail.v2beta.json
@@ -706,7 +706,7 @@
       }
     }
   },
-  "revision": "20210430",
+  "revision": "20210514",
   "rootUrl": "https://retail.googleapis.com/",
   "schemas": {
     "GoogleApiHttpBody": {
@@ -1610,7 +1610,7 @@
           "additionalProperties": {
             "$ref": "GoogleCloudRetailV2betaCustomAttribute"
           },
-          "description": "Highly encouraged. Extra product attributes to be included. For example, for products, this could include the store name, vendor, style, color, etc. These are very strong signals for recommendation model, thus we highly recommend providing the attributes here. Features that can take on one of a limited number of possible values. Two types of features can be set are: Textual features. some examples would be the brand/maker of a product, or country of a customer. Numerical features. Some examples would be the height/weight of a product, or age of a customer. For example: `{ \"vendor\": {\"text\": [\"vendor123\", \"vendor456\"]}, \"lengths_cm\": {\"numbers\":[2.3, 15.4]}, \"heights_cm\": {\"numbers\":[8.1, 6.4]} }`. This field needs to pass all below criteria, otherwise an INVALID_ARGUMENT error is returned: * Max entries count: 150 by default; 100 for Type.VARIANT. * The key must be a UTF-8 encoded string with a length limit of 128 characters.",
+          "description": "Highly encouraged. Extra product attributes to be included. For example, for products, this could include the store name, vendor, style, color, etc. These are very strong signals for recommendation model, thus we highly recommend providing the attributes here. Features that can take on one of a limited number of possible values. Two types of features can be set are: Textual features. some examples would be the brand/maker of a product, or country of a customer. Numerical features. Some examples would be the height/weight of a product, or age of a customer. For example: `{ \"vendor\": {\"text\": [\"vendor123\", \"vendor456\"]}, \"lengths_cm\": {\"numbers\":[2.3, 15.4]}, \"heights_cm\": {\"numbers\":[8.1, 6.4]} }`. This field needs to pass all below criteria, otherwise an INVALID_ARGUMENT error is returned: * Max entries count: 200 by default; 100 for Type.VARIANT. * The key must be a UTF-8 encoded string with a length limit of 128 characters.",
           "type": "object"
         },
         "availability": {
@@ -1687,7 +1687,7 @@
           "type": "string"
         },
         "type": {
-          "description": "Immutable. The type of the product. This field is output-only. Default to Catalog.product_level_config.ingestion_product_type if unset.",
+          "description": "Immutable. The type of the product. Default to Catalog.product_level_config.ingestion_product_type if unset.",
           "enum": [
             "TYPE_UNSPECIFIED",
             "PRIMARY",