dynamic_modules: enables rustfmt.toml

[mathetake]

Commit Message: dynamic_modules: enables rustfmt.toml Additional Description:

This enables the root configuration for rustfmt as a follow up on https://github.com/envoyproxy/envoy/pull/37070#discussion_r1845515368. Only formatting is done in this commit. There's no change in its code.

Risk Level: low Testing: n/a Docs Changes: n/a Release Notes: n/a Platform Specific Features: n/a [Optional Runtime guard:] [Optional Fixes #Issue] [Optional Fixes commit #PR or SHA] [Optional Deprecated:] [Optional API Considerations:]

[repokitteh-read-only[bot]]

As a reminder, PRs marked as draft will not be automatically assigned reviewers, or be handled by maintainer-oncall triage.

Please mark your PR as ready when you want it to be reviewed!

:cat:

Caused by: https://github.com/envoyproxy/envoy/pull/37295 was opened by mathetake. see: [more](https://github.com/envoyproxy/envoy/pull/37295), [trace](https://prod.repokitteh.app/traces/ui/envoyproxy/envoy/639d8100-a83e-11ef-8a87-265afa678815).

[mathetake]

cc @phlax

[soulxu]

/assign @mattklein123 @phlax