Feature: Group stacks by its agent

[ESPGranEdu]

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Description

I think that it would be nice when you have quite a few stacks defined across multiple agents (including the current), to have them grouped by it's agent.

In case that there aren't more agents configured, the UI will reamin exactly the same

Type of change

Please delete any options that are not relevant.

• User interface (UI)
• New feature (non-breaking change which adds functionality)

Checklist

• My code follows the style guidelines of this project
• I ran ESLint and other linters for modified files
• I have performed a self-review of my own code and tested it
• I have commented my code, particularly in hard-to-understand areas
  (including JSDoc for methods)
• My changes generate no new warnings
• My code needed automated testing. I have added them (this is optional task)

Screenshots (if any)