IssuesFieldExtension is a field extension for
the field issues of the type BoardList.
The extension is used to check and set
relative positions of returned issues.

Because IssuesFieldExtension needs to pass
a paginated list of issues to
::Boards::Issues::ListService.initialize_relative_positions
for performance, the extension needs to execute after
the underlying issues relation has been wrapped
by the default pagination connection extension.
We achieve this by utilizing 'late_extensions'
on initializing the field.

Previously we incorrectly called initialize_relative_position
by passing an underlying AR relation rather than
a paginated result when resolving the field in BoardListIssuesResolver.
This produced DB queries without `LIMIT` clause -
causing performance degradations.

Changelog: fixed