Lazy load pipeline actions

What does this MR do and why?

Lazy loads pipeline actions (manual/scheduled) instead of fetching them for every pipeline on load.

Screenshots or screen recordings

When limit is reached

**Note I changed limit to two temporarily to generate this screenshot. Limit is actually 50

How to set up and validate locally

1. Enable feature flag :lazy_load_pipeline_dropdown_actions in rails console
2. Visit Project > CI/CD > Pipelines
3. Ensure your pipeline has a manual job
4. Ensure manual actions are lazy loaded

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #336514 (closed)