[BUG] Style issue in Add Rule Flyout

[maryam-saeidi]

Copied from #145987

📝 Summary

Some pages under Observability App have a styling issue. Mostly margin and spacing issues.
The pages that are affected so far are:

• Rule flyout

It could be related to #144845

Note: This upgrade contains breaking changes to `EuiFlexGroup` and
`EuiFlexGrid,` primarily around switching margins and negative margins
to `gap.` Please do a quick QA pass of your app to scan for any issues.
We're happy to help resolve minor fixes or potentially follow up after
PR merges. You can find us over in #eui!

✅ AC

• Check the bug surface
• It seems that the BCs are safe. 8.6. to be verified
• Do the necessary fix

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)

[XavierM]

@jcger Can you look at this one?

[jcger]

@maryam-saeidi could you please check again? I merged a fix for this here #147001 and now that I checked again just in case everything seems to be ok

[maryam-saeidi]

@jcger Yes, in my recent branch, I saw the issue was fixed, thanks! 🙏🏻

Duplicate of #145999