Lookup: automatic v prefix detection/removal

[rarkins]

Describe the proposed change(s).

Reproduction repo: https://github.com/renovate-reproductions/27127

Type of problem to avoid: https://github.com/renovate-reproductions/27127/pull/1

We should detect if:

• currentValue has no v prefix
• currentVersion does have a v prefix (in the datasource result)

And if so then:

• strip the v prefix from newVersion, so that it is not part of newValue