Add retries for suitable package poll/publish error scenarios

[tom--pollard]

Currently errors which occur during polling or publishing at a package level are logged, resulting in a generic pollErr/pubErr, with the given packages data being lost whilst the remaining packages are processed.

There are various situations in which the error leading to the data loss could be from a transient problem (upstream feed registry issue, network blip sending the package json to the configured publisher etc) as such preventative measures such as controlled retries could reduce unnecessary data loss.