Refactor FXIOS-4905 [v106] Update nimbus experiments job step inputs and control flow

[jeddai]

A few changes are happening here:

• update the fetch depth to be 0 so it will fetch branches when cloning the repository
• update the version and inputs for the update experiments step
• update the create pull request step to make sure there are changes for the branch
• add the enable pull request automerge step
  • the automerge will only happen after all other branch protection points are met, such as an approving review

#11864

[isabelrios]

LGTM

[lmarceau]

Build is green here