[processor/transform] Fix basic config cache access

[edmocosta]

Description

This PR removes the shared cache logic we introduced to support Basic Config statements, and changes the approach to group all Basic config statements together into the same sharing-cache common.ContextStatements, embracing the limitation of not being able to infer the context depending on the user's statements (similar to the advanced config).
To help with that limitation, the context inferrer validation was improved, and it now returns specific errors that better describe why it couldn't infer a valid context.

This PR also introduces a breaking change, that consists in forcing users to use either basic or advanced configuration, for example, mixed configurations like the following won't be valid anymore, and it will require users to use only one style:

log_statements:
 - set(resource.attributes["foo"], "foo")
 - statements:
   - set(resource.attributes["bar"], "bar")

---

Another PR will be open for removing the WithCache option from all OTTL contexts.

Link to tracking issue

Fixes #38926

Testing

Unit tests

Documentation

Updated README

[TylerHelmuth]

@edmocosta can you add a new test somewhere, either in the transformprocessor or OTTL's e2e tests, for

log_statements:
      - merge_maps(log.cache, ParseJSON(log.body), "upsert") where IsMatch(log.body, "^\\{")
      - set(log.body, log.cache["log"])

[edmocosta]

Hi @TylerHelmuth, thanks for reviewing, I've added a few tests that although are using different statements, does check the exactly same condition.