Provide custom string replacement

You can provide custom string replacement information using the --replace flag. This flag takes a YAML file as input.

The YAML file should have the following structure:

- old: "this is old"
  new: "this is new string"
- old: "another old string"
  new: "another new string"

The usage of the flag is as follows:

harness-upgrade --load file.yaml --replace replace.yaml app --all