added Uniform as default multimapper option

[ekiernan]

Description

Turned on the multimapper "Uniform" option in the Optimus wdl by default.

Checklist

If you can answer "yes" to the following items, please add a checkmark next to the appropriate checklist item(s) and notify our WARP documentation team by tagging either @ekiernan or @kayleemathews in a comment on this PR.

• [ ] Did you add inputs, outputs, or tasks to a workflow?
• [ ] Did you modify, delete or move: file paths, file names, input names, output names, or task names?
• [ ] If you made a changelog update, did you update the pipeline version number?

[github-actions[bot]]

Remember to squash merge!

[github-actions[bot]]

Validation Results:

Comparing versions and changelogs for pipelines that differ from the versions on 'origin/develop':
PairedTag.wdl has not been changed and needs updating
Optimus.wdl has not had its version updated
Multiome.wdl has not been changed and needs updating
Some WDLs or changelog files need updating. See output for details.
validation_failed