Extend automation pallet to allow processing of paused transfers

[ebma]

Context

This is a follow-up for #357.

In #357, we implemented the processing of transfers so that the processing is paused when the designated exchange rate/amount cannot be achieved. To prevent transfers from getting stuck and users losing their funds, we need to extend the automation pallet to allow for the continuation of these paused transfers.

TODO

We should add a new extrinsic continueOfframpForReference(reference) which retries the processing of the offramp requests, re-checking if the buffer pool account holds enough tokens this time. The extrinsic is callable by any user.

For this to work, we assume that someone charged the pallet's buffer pool account in the meantime.

[prayagd]

Hey team! Please add your planning poker estimate with Zenhub @b-yap @bogdanS98 @ebma @gianfra-t @TorstenStueber

[TorstenStueber]

@prayagd we should move this to icebox.