feat: error-doc handling in python SDK

[drstrangelooker]

Lookups now take place against the CDN to find a more detailed error guide. The url to that error guide, and the error guide itself - a markdown document - are included in the SDKError class and the ErrorDetail class.

[drstrangelooker]

Sample output after adding some prints to test_connection.py

$ PYTHONPATH=~/sdk-codegen/python python test_connection.py foo
/usr/local/google/home/drstrangelove/.pyenv/versions/3.8.2/lib/python3.8/site-packages/urllib3/connectionpool.py:1103: InsecureRequestWarning: Unverified HTTPS request is being made to host 'localhost'. Adding certificate verification is strongly advised. See: https://urllib3.readthedocs.io/en/latest/advanced-usage.html#tls-warnings
  warnings.warn(
/usr/local/google/home/drstrangelove/.pyenv/versions/3.8.2/lib/python3.8/site-packages/urllib3/connectionpool.py:1103: InsecureRequestWarning: Unverified HTTPS request is being made to host 'localhost'. Adding certificate verification is strongly advised. See: https://urllib3.readthedocs.io/en/latest/advanced-usage.html#tls-warnings
  warnings.warn(
https://static-a.cdn.looker.app/errorcodes/404.md
## HTTP Status Code 404 - Not Found

## Description

A 404 Not Found error is the default error if anything goes wrong, usually with things like permissions. The response message for a 404 error provides minimal, if any, information. This is intentional, since 404 errors are shown to people with incorrect login credentials or insufficient permissions. Looker does not want to provide specific information in 404 response messages, since this information could be used to map out the "attack surface" of our API.

If API `/login` attempts are returning 404 errors, it's most likely because your API3 `client_id` or `client_secret` isn't valid (see [this section](https://docs.looker.com/reference/api-and-integration/api-troubleshooting#verify_your_api_credentials) of our API troubleshooting doc). The API login REST endpoint is one of the following, depending on the API version in use:

`https://<your-looker-hostname>:<port>/api/4.0/login`
`https://<your-looker-hostname>:<port>/api/3.1/login`

You can also get a 404 error after you log in. If you're logged in and you get a 404 error, that means you don't have permissions for the API command you just called.

## Resolution

* For a Swagger codegen client, the `base_url` should be one of the following, depending on the API version in use:
`https://<your-looker-hostname>:<port>/api/4.0/`
`https://<your-looker-hostname>:<port>/api/3.1/`

* If login is successful, verify that the logged in user has permissions to execute the given command in the UI.

## Reference

See the [Mozilla website](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/404) for more information on HTTP status code 404

See [Looker API Troubleshooting](https://cloud.google.com/looker/docs/reference/api-and-integration/api-troubleshooting) for more information on troubleshooting API errors in Looker
[]
Traceback (most recent call last):
  File "test_connection.py", line 80, in <module>
    main()
  File "test_connection.py", line 39, in main
    raise e
  File "test_connection.py", line 34, in main
    connection = get_connections(connection_name)
  File "test_connection.py", line 47, in get_connections
    connection = sdk.connection(name, fields="name, dialect")
  File "/usr/local/google/home/drstrangelove/sdk-codegen/python/looker_sdk/sdk/api40/methods.py", line 3534, in connection
    self.get(
  File "/usr/local/google/home/drstrangelove/sdk-codegen/python/looker_sdk/rtl/api_methods.py", line 157, in get
    return self._return(response, structure)
  File "/usr/local/google/home/drstrangelove/sdk-codegen/python/looker_sdk/rtl/api_methods.py", line 101, in _return
    raise sdk_error
looker_sdk.error.SDKError

[github-actions]

Python Tests

    9 files      9 suites   1m 46s ⏱️
144 tests 139 ✔️   5 💤 0 ❌
676 runs  657 ✔️ 19 💤 0 ❌

Results for commit a80f140.

[drstrangelooker]

Updated the SDKError and ErrorDoc objects with a __str__() method so that they automagically display some useful data.

looker_sdk.error.SDKError: 
    message:           Not found
    documentation_url: https://cloud.google.com/looker/docs/r/err/4.0/404/get/connections/:connection_name
    error_doc_url:     https://static-a.cdn.looker.app/errorcodes/404.md
    error details:

[github-actions]

Python Tests

    9 files      9 suites   1m 58s ⏱️
144 tests 139 ✔️   5 💤 0 ❌
676 runs  657 ✔️ 19 💤 0 ❌

Results for commit e264d2d.

[github-actions]

Python Tests

    8 files      8 suites   1m 19s ⏱️
144 tests 138 ✔️   5 💤 0 ❌ 1 🔥
653 runs  634 ✔️ 18 💤 0 ❌ 1 🔥

For more details on these errors, see this check.

Results for commit e89193c.

[github-actions]

Python Tests

    9 files      9 suites   1m 45s ⏱️
144 tests 139 ✔️   5 💤 0 ❌
676 runs  657 ✔️ 19 💤 0 ❌

Results for commit e89193c.

[jkaster]

This is a slightly different implementation than we have for other SDKs due to needing to keep SDKs like TS as lean as possible, but this feels like it could be a good approach for the Python SDK, and perhaps some of the others. Will consider it for other SDK implementations.