Better logging of API errors

[vprivat-ads]

In case GITHUB_TOKEN is undefined and we have exceeded our anonymous rate limit, we get the following output:

/home/xxx/projects/stac/stac-extensions.github.io/python/create_readme.py:19: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
  logger.warn("No GITHUB_TOKEN found in env")
No GITHUB_TOKEN found in env
response invalid
response invalid
Traceback (most recent call last):
  File "/home/xxx/projects/stac/stac-extensions.github.io/python/create_readme.py", line 185, in <module>
    main()
  File "/home/xxx/projects/stac/stac-extensions.github.io/python/create_readme.py", line 166, in main
    data = get_extensions()
           ^^^^^^^^^^^^^^^^
  File "/home/xxx/projects/stac/stac-extensions.github.io/python/create_readme.py", line 71, in get_extensions
    data = get_sources()
           ^^^^^^^^^^^^^
  File "/home/xxx/projects/stac/stac-extensions.github.io/python/create_readme.py", line 58, in get_sources
    data.append(from_gh(repo.json(), True))
                ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/xxx/projects/stac/stac-extensions.github.io/python/create_readme.py", line 23, in from_gh
    "title": response["name"],
             ~~~~~~~~^^^^^^^^
KeyError: 'name'

With this PR we get a more user-friendly output:

No GITHUB_TOKEN found in env
stac-extensions not available: 403 Client Error: rate limit exceeded for url: https://api.github.com/users/stac-extensions/repos?per_page=1000
community repo not available: 403 Client Error: rate limit exceeded for url: https://api.github.com/repos/crim-ca/dlm-extension
community repo not available: 403 Client Error: rate limit exceeded for url: https://api.github.com/repos/Terradue/stac-extensions-disaster
community repo not available: 403 Client Error: rate limit exceeded for url: https://api.github.com/repos/openrsgis/trainingdml-ai-extension
community repo not available: 403 Client Error: rate limit exceeded for url: https://api.github.com/repos/stacchain/merkle-tree
community repo not available: 403 Client Error: rate limit exceeded for url: https://api.github.com/repos/IFRCGo/monty-stac-extension
Something likely went wrong as there are not enough repos listed, don't override README