Oracles: unbounded feed values vector

[lemunozm]

The current oracle's extrinsic feed_values() allows an unbounded Vec as an input parameter. This would allow a member to act badly generating a huge list of values that fill the block computation time for free, because the member is not paying fees under success.

Even if all OracleKey possible values are limited, the vector can still contain duplicates that must be iterated, consuming, in the worst case, the entire block available time.

We think the solution to this is as simple as making this Vec bounded. If you agree, I can add a PR with this change.

[xlc]

I agree. It is usually a good idea to make vec bounded anyway.