Icons - add support for custom icons

Is this a new component or an extension of an existing one?
What is the existing component, if any?

Existing, MenuToggle, ToolbarFilter

When using PF tokens to create a custom theme, MenuToggle and ToolbarFilter use default icons in PF that currently cannot be changed via a prop since the prop does not exist, while components like Label, Alert, and Button, offer this functionality.

An alternative option was discussed at today's working session (cc @mcoker), which would include adding support for custom icons directly to react-icons and then importing any custom overrides.

Related: https://github.com/patternfly/patternfly-react/issues/10634

Describe the feature
A clear and concise description of the new feature. What is the expected behavior?

Are there visuals for this feature? If applicable, please include examples for each state and for varying widths

See below. MUI uses a different toggle icon for their menu toggle.

Include screenshots or links to Marvel or other mockups.
MUI:

PF:

Any other information?
Would it be possible to prioritize this work for an upcoming sprint to align with RHOAI priorities for the MUI theming effort @nicolethoen ?

Beginne damit, die Implementierungen der Komponenten MenuToggle und ToolbarFilter zu überprüfen, und lies anschließend Issue #10634 sowie die Diskussion über die Erweiterung von react-icons. Als abgeschlossen gilt die Aufgabe, wenn Benutzer über eine vereinbarte, dokumentierte API benutzerdefinierte Symbole für beide Komponenten bereitstellen können und sich das Verhalten an der bestehenden Symbolunterstützung in Label, Alert und Button orientiert.