feat(header): add translucent support on ionic theme (#30493)

Issue number: internal

---------

<!-- Please do not submit updates to dependencies unless it fixes an
issue. -->

<!-- Please try to limit your pull request to one type (bugfix, feature,
etc). Submit multiple pull requests if needed. -->

## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

When using ionic theme there's no support for translucent prop on the
ion-header.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

- Add support for translucent prop on Ionic theme
- Adjusted tests to also run for ionic-md 

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

<!--
  If this introduces a breaking change:
1. Describe the impact and migration path for existing applications
below.
  2. Update the BREAKING.md file with the breaking change.
3. Add "BREAKING CHANGE: [...]" to the commit description when merging.
See
https://github.com/ionic-team/ionic-framework/blob/main/docs/CONTRIBUTING.md#footer
for more information.
-->


## Other information

<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->

[Ionic header
fade](https://ionic-framework-git-rou-11911-ionic1.vercel.app/src/components/header/test/fade?ionic:theme=ionic)

---------

Co-authored-by: ionitron <hi@ionicframework.com>