feat(progress-bar): Missing `--mdc-linear-progress-active-indicator-shape` property for progress-bar

### Feature Description

Currently if I want to change the shape of the progress bar to be round like, I only have the `--mdc-linear-progress-track-shape` to set the track shape, but not the same option for the shape of the active-indicator, which will still be square.
Also, only setting the `--mdc-linear-progress-track-shape`, will result in the active indicator overflowing, leaving me with an inconsistent progress-bar (see 1st picture)

Hence that leaves me with the better option of just setting the `border-radius` of the `mat-progress-bar` element itself, because this doesn't cause the active-indicator to overflow. In this case the `--mdc-linear-progress-track-shape` becomes redundant.

1. Screenshot with `--mdc-linear-progress-track-shape: 4px;`, causing the active-indicator to overflow:

2. Screenshot with `--mdc-linear-progress-track-shape: 4px;` and `border-radius: 4px`, rendering the `--mdc-linear-progress-track-shape` redundant:

3. Screenshot with only `border-radius: 4px;` leaving me with an almost round progress bar, except that the active-indicator is not actually round.

So there need to be an option to set the `--mdc-linear-progress-active-indicator-shape` like for other components, so that the active-indicator can be made round, as shown in the [Token and Specs section in the Material 3 specification](https://m3.material.io/components/progress-indicators/specs)

### Use Case

This would enable a very relevant an normal use case that is also shown in the [Token and Specs section in the Material 3 specification](https://m3.material.io/components/progress-indicators/specs).

Inizia con il componente progress-bar e traccia come --mdc-linear-progress-track-shape viene applicato al track e all’active indicator. Confronta lo stile con la sezione Token and Specs di progress-indicator di Material 3, quindi verifica che la nuova active-indicator shape option arrotondi l’indicatore senza overflow.

Scritto dal modello di indicizzazione a partire dal testo della issue.