Support Ollama LLM model pulling

[devtobi]

I want to suggest a new step

• Which tool is this about? Where is its repository?
  I want topgrade to support ollama, a tool for managing LLMs locally, see https://github.com/ollama/ollama.
  Topgrade should invoke model pulling to update all locally installed models.

• Which operating systems are supported by this tool?
  Windows, macOS, Linux

• What should Topgrade do to figure out if the tool needs to be invoked?
  if ollama is found in path it should be invoked, this also has to work when ollama was installed through package managers like homebrew.

• Which exact commands should Topgrade run?
  I am currently running through a custom command with ollama list | awk 'NR>1 && !/reviewer/ {system(\"ollama pull \"$1)}'
  This allows to pull all new model files for currently installed models.
  I am not sure if this command works OS independent.

• Does it have a --dry-run option? i.e., print what should be done and exit
  No dry run option available

• Does it need the user to confirm the execution? And does it provide a --yes
  option to skip this step?
  No user confirmation needed

More information

To test this a model should be downloaded on the local machine first, e.g. via ollama run qwen2.5-coder:0.5b.
When topgrade invokes ollama it should show an output similar to

pulling manifest
pulling 170370233dd5... 100% ▕████████████████████████████████████████████████████▏ 4.1 GB
pulling 72d6f08a42f6... 100% ▕████████████████████████████████████████████████████▏ 624 MB
pulling 43070e2d4e53... 100% ▕████████████████████████████████████████████████████▏  11 KB
pulling c43332387573... 100% ▕████████████████████████████████████████████████████▏   67 B
pulling ed11eda7790d... 100% ▕████████████████████████████████████████████████████▏   30 B
pulling 7c658f9561e5... 100% ▕████████████████████████████████████████████████████▏  564 B
verifying sha256 digest
writing manifest
success