[Streams] Downsampling flyout fixes

[damian-polewski]

Closes #252545

Summary

This PR fixes issues with EditIlmPhasesFlyout and EditDslStepsFlyout components listed below:

• (ILM) Hide the readonly field when the downsampling is enabled. - Create edit ILM flow #253393 (comment)
• (ILM) Fix the default values for min_age and fixed_interval in ILM flyout. - Create edit ILM flow #253393 (comment)
• (ILM/DSL) Add debounce to onChange. - Create edit ILM flow #253393 (comment)
• (ILM/DSL) Fix issue with Save button being enabled when errors are present. - Create edit ILM flow #253393 (comment)
• (ILM/DSL) Fix border color on tabs with errors. - Create edit ILM flow #253393 (comment)
• (ILM/DSL) Fix add button color to text. - Create edit ILM flow #253393 (comment)
• (ILM/DSL) Add a tooltip to Save button when it's disabled due to form errors. - Create edit ILM flow #253393 (comment)
• (ILM) Fix issue with min_age validation when clearing validated input - Create edit ILM flow #253393 (review)

Checklist

Check the PR satisfies following conditions.

Reviewers should verify this PR satisfies this list as well.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the docker list
• This was checked for breaking HTTP API changes, and any breaking changes have been approved by the breaking-change committee. The release_note:breaking label should be applied in these situations.
• Flaky Test Runner was used on any tests changed
• The PR description includes the appropriate Release Notes section, and the correct release_note:* label is applied per the guidelines
• Review the backport guidelines and apply applicable backport:* labels.

[elasticmachine]

Pinging @elastic/kibana-management (Team:Kibana Management)

[SoniaSanzV]

Thank you for the fixes, I found a bug in the Dsl flyout. If a step has errors and I click add another one with the error still present, the save button gets enabled when the new step is added

Screen.Recording.2026-02-20.at.15.31.15.mov

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 67461b5

Failed CI Steps

• Jest Tests #2
• Jest Integration Tests #6
• Jest Integration Tests #8

Test Failures

• [job] [logs] Jest Tests #2 / Header QueryTabHeader should render the immutable timeline call out providers
• [job] [logs] Jest Integration Tests #6 / ui settings migrations migrates siem:* configs

Metrics [docs]

✅ unchanged

cc @damian-polewski

[SoniaSanzV]

Thank you for addressing all this, lgtm :)