agent init: Generate without secrets by default

[discordianfish]

This closes #28

Without --secret:

agent init /tmp/foo
caller=generator.go:60 level=info msg="can't find local diambra-arena version, using latest" err="exit status 1"
caller=generator.go:66 level=debug msg="using diambra-arena version" version=2.1.0rc1
🖥️  Creating requirements.txt
🖥️  Creating agent.py
🖥️  Creating README.md
🖥️  Creating Dockerfile
🖥️  Agent initialized in /tmp/foo

Then if run with --secret it will show the diff and prompt to overwrite. I don't think automatically changing the files is reliably enough to not make it more confusing. I would expect users to either just overwrite the files, or skip them and do the changes manually. A nicer diff output would be great, especially the char-by-char diffs is confusing. I've filled #19 for that already but thats something for later.

Here is the current output:

[alexpalms]

@discordianfish This looks perfect! Let s merge it!