Add "Salesforce Object Metadata" action

Problem/Motivation

Dynamic workflows need access to Salesforce object metadata to determine available fields and their properties.

Use cases:
- Discover fields available on custom objects
- Check field properties before operations
- Build dynamic forms based on Salesforce schema
- Validate data before pushing to Salesforce

Steps to reproduce

1. Create an ECA model
2. Need to get field information for a Salesforce object
3. No action available to retrieve object metadata

Proposed resolution

Add an action that retrieves object metadata from Salesforce using the objectDescribe() method.

Remaining tasks

- [ ] Create action plugin
- [ ] Call objectDescribe() API method
- [ ] Parse and structure metadata
- [ ] Store field information in tokens
- [ ] Test with standard and custom objects

User interface changes

New action "Get Salesforce object metadata" will appear in ECA.

API changes

None.

Data model changes

None.