[Backport 2.x] Fixing ProvisionWorkflowTransportAction, handling case in which a document does not exist

[opensearch-trigger-bot]

Backport 63ef780 from #100.

[joshpalis]

/home/runner/work/opensearch-ai-flow-framework/opensearch-ai-flow-framework/src/main/java/org/opensearch/flowframework/workflow/RegisterModelStep.java:142: error: cannot find symbol

            machineLearningNodeClient.register(mlInput, actionListener);
                                     ^
  symbol:   method register(MLRegisterModelInput,ActionListener<MLRegisterModelResponse>)
> Task :compileJava
  location: variable machineLearningNodeClient of type MachineLearningNodeClient
/home/runner/work/opensearch-ai-flow-framework/opensearch-ai-flow-framework/src/main/java/org/opensearch/flowframework/workflow/DeployModelStep.java:73: error: cannot find symbol

        machineLearningNodeClient.deploy(modelId, actionListener);
                                 ^
> Task :compileJava FAILED
  symbol:   method deploy(String,ActionListener<MLDeployModelResponse>)
  location: variable machineLearningNodeClient of type MachineLearningNodeClient
2 errors

Seems that ML-commons did not backport register and deploy into 2.11 before cutting the branch. Will have to bump up our 2.x version to 2.12

[codecov]

Codecov Report

Merging #102 (7ca967b) into 2.x (19c8935) will decrease coverage by 0.37%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##                2.x     #102      +/-   ##
============================================
- Coverage     81.82%   81.46%   -0.37%     
  Complexity      285      285              
============================================
  Files            30       30              
  Lines          1117     1122       +5     
  Branches        125      126       +1     
============================================
  Hits            914      914              
- Misses          158      162       +4     
- Partials         45       46       +1     

Files	Coverage Δ
...rk/transport/ProvisionWorkflowTransportAction.java	45.61% <0.00%> (-4.39%)	⬇️