Doc Update: Add Session OpProcessor close message back to Provider Documentation

[xiazcy]

The close message for drivers was added back in 3.5.2 (https://issues.apache.org/jira/browse/TINKERPOP-2660), but wasn't added back in provider docs for 3.5.2+. Updated provider docs for the message based on the changes.

[codecov-commenter]

Codecov Report

Merging #1706 (cc74002) into master (287499e) will increase coverage by 0.41%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1706      +/-   ##
==========================================
+ Coverage   63.35%   63.76%   +0.41%     
==========================================
  Files          23       23              
  Lines        3553     3596      +43     
==========================================
+ Hits         2251     2293      +42     
- Misses       1129     1139      +10     
+ Partials      173      164       -9     

Impacted Files	Coverage Δ
gremlin-go/driver/client.go	79.12% <0.00%> (-3.30%)	⬇️
gremlin-go/driver/gorillaTransporter.go	61.81% <0.00%> (-2.73%)	⬇️
gremlin-go/driver/graphTraversal.go	88.02% <0.00%> (-1.09%)	⬇️
gremlin-go/driver/serializer.go	64.76% <0.00%> (ø)
gremlin-go/driver/graphBinary.go	53.89% <0.00%> (+0.09%)	⬆️
gremlin-go/driver/traversal.go	71.42% <0.00%> (+0.88%)	⬆️
gremlin-go/driver/strategies.go	67.88% <0.00%> (+2.18%)	⬆️
gremlin-go/driver/graphTraversalSource.go	83.16% <0.00%> (+2.26%)	⬆️
gremlin-go/driver/protocol.go	66.40% <0.00%> (+3.20%)	⬆️
gremlin-go/driver/anonymousTraversal.go	46.66% <0.00%> (+4.34%)	⬆️

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[spmallette]

cherry-picked as 0a57213