Use ML Commons validation methods in workflow parsing

[dbwiddis]

Description

Resolves #1152.

Adds field value validation during workflow template validation (validation=all) using ML Commons StringUtils.validateFields(). This catches invalid characters in name and description fields at parse time rather than waiting for runtime provisioning failures.

Validated steps

The following ML Commons steps now have name/description validated during workflow parsing, matching the validation added in ml-commons#3805:

Step	name (required)	description (optional)
create_connector	✅	✅
register_remote_model	✅	✅
register_local_custom_model	✅	✅
register_local_sparse_encoding_model	✅	✅
register_local_pretrained_model	✅	✅
register_model_group	✅	✅

Changes

• WorkflowProcessSorter.java: Added validateFieldValues() method called from validate(). Uses StringUtils.validateFields() and FieldDescriptor from ML Commons directly — no duplicated validation logic.
• WorkflowProcessSorterTests.java: Added 4 tests covering valid inputs, invalid name, invalid description, and non-ML step passthrough.

Design decisions

• Only validates literal string values in user inputs. Fields provided via previous_node_inputs (runtime references) are not validated at parse time.
• Substitution template fields (e.g., ${{name}}) are also not validated, as these are resolved at provisioning time with user-supplied values.
• Uses the same FieldDescriptor required/optional semantics as ML Commons: name is required, description is optional.
• Error messages include the step label and node ID for easy debugging.
• Agent and tool steps are not included because ML Commons does not yet validate those (see jngz-es comment on #3805).

How to test

# Create a workflow with an invalid connector name
POST _plugins/_flow_framework/workflow?validation=all
{
  "name": "test",
  "workflows": {
    "provision": {
      "nodes": [{
        "id": "create_connector",
        "type": "create_connector",
        "user_inputs": {
          "name": "Bad<script>Name",
          "description": "test",
          "version": "1",
          "protocol": "http",
          "parameters": {},
          "credential": {},
          "actions": []
        }
      }]
    }
  }
}
# Should return 400 with validation error about connector name

Check List

• New functionality includes testing.
• Commits are signed per the DCO using --signoff.

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[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.56%. Comparing base (69f83e2) to head (5bf02ee).

Files with missing lines	Patch %	Lines
.../flowframework/workflow/WorkflowProcessSorter.java	90.90%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1368      +/-   ##
============================================
+ Coverage     78.38%   78.56%   +0.17%     
- Complexity     1308     1315       +7     
============================================
  Files           106      106              
  Lines          6019     6041      +22     
  Branches        641      647       +6     
============================================
+ Hits           4718     4746      +28     
+ Misses         1012     1004       -8     
- Partials        289      291       +2     

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