[processor/transform] Add support for global condition's fully qualified paths and error mode overrides

[edmocosta]

Description

This PR is part of #29017, and a split from #36888. It changes the transformprocessor, adding support for error mode overrides per context statements group, and global conditions with fully qualified paths for context-inferred configuration styles.

Change log:

• Structured context-inferred configuration styles (without context: <value>) now supports and requires conditions with fully qualified paths, for example:

  log_statements:
    - statements:
        - set(log.attributes["pass"], "true")
      conditions:
        - log.attributes["pass"] == nil
  

  If non qualified paths are used, it raises an error, for example - attributes["pass"] == nil would generate the following error:

  invalid config for "transform" processor unable to parse OTTL condition "attributes[\"pass\"] == nil": missing context name for path "attributes[pass]", possibly valid options are: "log.attributes[pass]", "instrumentation_scope.attributes[pass]", "resource.attributes[pass]"
  

  Existing non-context inferred configurations shouldn't be impacted by this change.

• A new configuration error_mode key has been added to the context statements group (common.ContextStatements),
  When provided, it overrides the top-level error mode, offering more granular control over error handling, for example:

   error_mode: propagate
   log_statements:
     - context: log
       error_mode: ignore
       statements: 
         - set(attributes["attr1"], ParseJSON(1))
     - context: log
       statements:
         - set(attributes["executed"], true)

Link to tracking issue

#29017

Testing

Unit tests

Documentation

Changed the README to include the new configuration key error_mode

[evan-bradley]

Nice! My comments are only nits.