Configuration for formatting Throwable stack traces

I'd like to see more options for how stack traces are formatted in the ECS logs to help in reducing the size of logs.

Some examples:

1. Maximum depth
2. Include/exclude stack frames based on a pattern
3. Shorten class names by abbreviating package names to fit within a specified length
4. Root cause first or last

Ideally a configuration option could override the formatting of the stack trace through an interface implementation provided by the application. That implementation could return a `String[]` or `Stream` of the formatted stack frames which are then added to the ECS log either as a JSON string or an array of strings.

I'd be happy to work on a PR for this if there is interest in it being included.

Start by locating the existing ECS Throwable stack-trace formatter and its configuration path. Compare the requested depth, frame filtering, class-name shortening, root-cause ordering, and application-provided formatter interface with the current behavior. Done requires an agreed scope and tests for the selected formatting options and output shapes.

Written by the indexing model from the issue text.