amp-fit-text customize justify-content

### Description

Hey Everyone,

I want to be able to set `justify-content` on the `amp-fit-text` element. In my case, I would like `justify-content: flex-start`. (Of course this would get overridden if there is overflowing text and that is OKAY).

In PR #32588 [amp-fit-text:1.0 Vertical center non-overflowing text](https://github.com/ampproject/amphtml/pull/32558) the `amp-fit-text` component was updated to always use `justify-content: center`. It looks like this was done so that `1.0` would have the same functionality as `0.1`.

Perhaps there is a good way to customize the `amp-fit-text` component `justify-content` style? Open to ideas to submit a PR.

### Reproduction Steps

Here is what I am currently seeing with `justify-content: center`.

Setting `justify-content: flex-start` on the shadow DOM gives this

### Relevant Logs

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### Browser(s) Affected

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### OS(s) Affected

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### Device(s) Affected

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### AMP Version Affected

1.0

Start by reviewing the amp-fit-text component and the behavior introduced in PR #32588, especially the change that forces justify-content to center. Determine how a caller could customize that alignment while preserving the existing overflowing-text behavior. Done means non-overflowing text can use a requested value such as flex-start without breaking the component's current overflow handling.

Written by the indexing model from the issue text.