Add prerelease support to 'simple' release types

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**Is your feature request related to a problem? Please describe.**
I have been attempting to create prereleases based on a monorepo, which uses the 'simple' release strategy, however this does not work.

**Describe the solution you'd like**
I would like for support to be added for prerelease in 'simple' release types. Additionally, to not have to add a suffix to prereleases (e.g. '-alpha01'), so that releases can simply be toggled to 'latest' without needing to modify the names.

**Describe alternatives you've considered**
Currently I have to set up a separate GitHub actions workflow to convert all releases created by release-please back to pre-releases, which is not a cohesive process

**Additional context**
N/A