Enable Subscription Functionality for GraphiQL-Explorer

[fabiangfd]

The way GraphiQL-Explorer is currently initialized by Ariadne, subscriptions do not work.

This pull request allows to set the subscription endpoint (to be used by GraphiQL) manually via a subscription_url-parameter, which defaults to a websocket connection at the location of the graphiql-explorer (e.g., ws://localhost:8000/graphql/, if the explorer is reached via http://localhost:8000/graphql/).

[rafalp]

Tests are failing. Can you fix them?

[codecov]

Codecov Report

Merging #1125 (e386d27) into master (48fd7c7) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head e386d27 differs from pull request most recent head 3cfd93b. Consider uploading reports for the commit 3cfd93b to get more accurate results

@@           Coverage Diff           @@
##           master    #1125   +/-   ##
=======================================
  Coverage   97.82%   97.82%           
=======================================
  Files         115      115           
  Lines        7763     7767    +4     
=======================================
+ Hits         7594     7598    +4     
  Misses        169      169           

Files	Coverage Δ
ariadne/explorer/graphiql.py	100.00% <ø> (ø)
tests/asgi/snapshots/snap_test_explorer.py	100.00% <ø> (ø)
tests/explorers/snapshots/snap_test_explorers.py	100.00% <100.00%> (ø)
tests/explorers/test_explorers.py	100.00% <100.00%> (ø)
tests/wsgi/snapshots/snap_test_explorer.py	100.00% <ø> (ø)

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[fabiangfd]

OK, I have fixed the tests: Added the new expected html from graphiql-explorer to the test snapshots.

[rafalp]

There's also a test for passing options to graphiQL explorer. Can you add one more for custom subscription url?

https://github.com/mirumee/ariadne/blob/master/tests/explorers/test_explorers.py#L19

[fabiangfd]

OK, I have added the test:
https://github.com/fabiangfd/ariadne/blob/master/tests/explorers/test_explorers.py#L24

[rafalp]

Thank you for contributing. This will need to have an changelog entry and documentation updated, but I'll handle those before next release.