add ProjectSliceToMap function

[Diaphteiros]

What this PR does / why we need it:
Adds a ProjectSliceToMap function.

Which issue(s) this PR fixes:
None

Special notes for your reviewer:

Release note:

Added a `ProjectSliceToMap` function to the `pkg/collections` package. This is useful for turning lists with identifiable items into maps with the identifiers as key, for example.

For better naming consistency, `ProjectSlice` has been renamed to `ProjectSliceToSlice`. The old function is deprecated and will be removed in the future.