`tonic-types` should add case to handle unknown custom error details

## Feature Request

### Crates

`tonic-types`

### Motivation

Currently if a error details type URL is not recognized, it is dropped on the floor and not included in the array of error details messages:

https://github.com/hyperium/tonic/blob/689a86dbad107fa721714bb02e7f8e39264a377d/tonic-types/src/richer_error/mod.rs#L838-L841

According to [Google AIP 193](https://github.com/aip-dev/google.aip.dev/blob/becf861c4d97ed7ed0ba4206c8945184ce3cdeff/aip/general/0193.md?plain=1#L75-L77), `Status::details` **should**, not must, use the standard detail payloads.

### Proposal

- Add a list container to hold the unknown error details serialized bytes in [`ErrorDetails`](https://github.com/hyperium/tonic/blob/689a86dbad107fa721714bb02e7f8e39264a377d/tonic-types/src/richer_error/error_details/mod.rs#L17-L47).
- Add a function to return `Option` of the custom error details by URL

### Alternatives

Considered just returning the raw bytes instead of `Any` in case the user uses `prost-wkt-types::Any`, or some other implementation, but it probably doesn't matter since it should be trivial to convert the type.