Add 'resume training' feature

[CBroz1]

Our current draft manages config.yaml within the dataframe, but doesn't make adjustments to the model training file located under models: <project_folder>/dlc-models/iteration-<#>/<scorer>/train/pose_cfg.yaml

To resume training from the previous training snapshot, we would need to modify the init_weights value to a full path without extension dlc-models/iteration-<#>/<scorer>/train/snapshot-<#>

[CBroz1]

partially addressed in upcoming workflow pr

[CBroz1]

This function provides the ability to update the training config file to point to the relevant checkpoint. The team will consider migrating this code to the element itself.