Improve the output of help, prompts, and so on for `databricks bundle
init` and the default template.
Among other things, this PR adds support for a new `welcome_message`
property that lets a template print a custom message on success:
```
$ databricks bundle init
Template to use [default-python]:
Unique name for this project [my_project]: lennart_project
Include a stub (sample) notebook in 'lennart_project/src': yes
Include a stub (sample) Delta Live Tables pipeline in 'lennart_project/src': yes
Include a stub (sample) Python package in 'lennart_project/src': yes
✨ Your new project has been created in the 'lennart_project' directory!
Please refer to the README.md of your project for further instructions on getting started.
Or read the documentation on Databricks Asset Bundles at https://docs.databricks.com/dev-tools/bundles/index.html.
```
---------
Co-authored-by: shreyas-goenka <88374338+shreyas-goenka@users.noreply.github.com>
Lennart Kats (databricks)