Add `EntryRecordMode` for storing checksum of request body only

Similar to [this PR](https://github.com/Azure/azure-sdk-for-java/pull/34631/files).

During recording, an incoming request can append header `x-recording-skip` with one of two values:

- `request-body` -> don't record body of this request
- `request-response` -> don't record this request at all

This issue covers a third option:

- `request-body-checksum` (naming pending feedback)

This should be similar to `request-body` in that the body itself should not be recorded. Instead, we should place the `checksum` of the received body where the body exists. This will enable `playback` systems to verify the _content_ during playback even if they're not storing the raw data.

CC @samvaity for visibility

Start with the linked Java PR and the EntryRecordMode concept, then trace where x-recording-skip values are handled during recording and playback. Confirm how request-body is represented and where a checksum would replace the body; done means supporting request-body-checksum without storing raw body data and enabling playback verification.

Written by the indexing model from the issue text.