feat: upgrade OpenAPI Generator 6.0.1 -> 7.11.0

This is not the latest version, but a version that does not
significantly change the generated types (newer versions lead to
some significant renames which make the change even bigger).

Changes needed:
- change `from gooddata_api_client.model.`
  to `from gooddata_api_client.models.`
- change `from gooddata_api_client import apis`
  to `from gooddata_api_client import api`
- remove `_preload_content`, there are now special methods with
  `_without_preload_content` suffix
- remove `_check_type` and `_return_http_data_only`
- replace `_from` with `var_from` for filters
- replace OpenApiModel by BaseModel as OpenApiModel is no longer
  generated
- add pydantic as a test-requirement
- fix _create_export: the response is no longer a dict
- fix SimpleMetric: it needs to use the Core identifier types

JIRA: CQ-1614
risk: low

Author: no23reason

.openapi-generator/custom_templates/configuration.mustache

@@ -1,3 +1,5 @@
+# coding: utf-8
+
 {{>partial_header}}
 
 from setuptools import setup, find_packages  # noqa: H301
@@ -19,18 +21,21 @@ VERSION = "{{packageVersion}}"
 # http://pypi.python.org/pypi/setuptools
 
 REQUIRES = [
-  "urllib3 >= 1.25.3",
-  "python-dateutil",
+    "urllib3 >= 1.25.3, < 3.0.0",
+    "python-dateutil >= 2.8.2",
 {{#asyncio}}
-  "aiohttp >= 3.0.0",
+    "aiohttp >= 3.8.4",
+    "aiohttp-retry >= 2.8.3",
 {{/asyncio}}
 {{#tornado}}
-  "tornado>=4.2,<5",
+    "tornado>=4.2, < 5",
 {{/tornado}}
 {{#hasHttpSignatureMethods}}
-  "pem>=19.3.0",
-  "pycryptodome>=3.9.0",
+    "pem >= 19.3.0",
+    "pycryptodome >= 3.9.0",
 {{/hasHttpSignatureMethods}}
+    "pydantic >= 2",
+    "typing-extensions >= 4.7.1",
 ]
 
 setup(
@@ -41,7 +46,7 @@ setup(
     author_email="{{infoEmail}}{{^infoEmail}}team@openapitools.org{{/infoEmail}}",
     url="{{packageUrl}}",
     keywords=["OpenAPI", "OpenAPI-Generator", "{{{appName}}}"],
-    python_requires=">=3.6",
+    python_requires=">=3.8",
     install_requires=REQUIRES,
     packages=find_packages(exclude=["test", "tests"]),
     include_package_data=True,