IK Fast Plugin : Yaskawa Motoman GP8 + FT Sensor + End Effector

1. Add the package to the .external_repos.yaml file in the main repository. Always pin a specific commit, don't use a branch unless the repository is owned by us.

   aa_ikfast_plugin:
    type: git
    url: https://github.com/additiveautomations/aa_ikfast_plugin.git
    version: b7973eeaf564806ee938a13528204b96ae89d657

2. Import make import-external-repos
3. ls external/src/ check new repository has been downloaded make shell
4. In the shell switch to the external motoman_gp8_arm_only_ikfast_plugin