fix: Support making Relay edges node NonNull (#968)

[gurobokum]

Support pointing edge and edge node as NonNull when using Relay Connections

class UserPhotosConnection(Connection):
    class Meta:
        node = UserPhoto

    class Edge:
        class Meta:
            required = True   # marks edge as NonNull
            node_required = True  # marks node as NonNull

Main issue: #968
Related issues: mcabrams/doppelganger#64, graphql-python/graphene-sqlalchemy#310

[codecov]

Codecov Report

Base: 95.98% // Head: 95.99% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (c8c7b68) compared to base (340d5ed).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1493      +/-   ##
==========================================
+ Coverage   95.98%   95.99%   +0.01%     
==========================================
  Files          51       51              
  Lines        1742     1747       +5     
==========================================
+ Hits         1672     1677       +5     
  Misses         70       70              

Impacted Files	Coverage Δ
graphene/relay/connection.py	100.00% <100.00%> (ø)

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[erikwrede]

Thank your for taking the time to put this together! This will be useful for everyone using codegen until graphql/graphql-spec#867 is merged into the GQL-Spec. ☺️

Can you please merge the new tests into the existing connection tests? It will be easier to find that way, as issue tests usually refer to specific bugs, but this is a feature that belongs to the core implementation.

[erikwrede]

This was superseded by #1504 and is released in 3.3.0 😊