Add profile-specific output_directory

[lcawl]

Background

This is a follow-up to #3985 and #3984

Per #3856 (comment) the changes in #3856 meant that it was no longer possible to use profiles to generate multiple bundles in unique directories in a single repo. This is necessary for repos that have multiple release note pages and changelog directives that reference local bundles. None of the currently-migrated Elastic release note pages are in this situation anymore (they're all using bundles derived from the CDN), however it is a breaking change and IMO should be fixed. Otherwise we need to clearly call this out as a method that's no longer supported.

Summary

Adds profile-specific output_directory.

Details

• A profile output_directory replaces bundle.output_directory for that profile (same as option-mode --output when it is a directory). The file is still {repo}-{product}-{version}.yaml.
• A .yml/.yaml value is a hard error; output: stays a hard error.
• --plan uses the same path.
• changelog upload (without --directory) scans the global output dir and each profile output_directory, each non-recursively.

docs-actions still needs no code change; only README wording there is a separate follow-up: elastic/docs-actions#320

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

• Yes
• No

2. If you answered "Yes" to the previous question, please specify the tool(s) and model(s) used (e.g., Google Gemini, OpenAI ChatGPT-4, etc.).

Tool(s) and model(s) used: Cursor Grok 4.6