[ENHANCEMENT] percli dac setup adds output dir to .gitignore

[AntoineThebaud]

Description

Just a simple addition to avoid further manual steps to the DaC users.
This step is skipped if the .gitignore file is not already present.

Checklist

• Pull request has a descriptive title and context useful to a reviewer.
• Pull request title follows the [<catalog_entry>] <commit message> naming convention using one of the
  following catalog_entry values: FEATURE, ENHANCEMENT, BUGFIX, BREAKINGCHANGE, DOC,IGNORE.
• All commits have DCO signoffs.

[AntoineThebaud]

'should make this idempotent by adding a check to avoid appending to gitignore if the built folder is already listed.

[celian-garcia]

If you want my opinion, I'm not fan of pre-assuming that the user of your tool want to create a git repo, or want to use git as a version manager or even want to ignore the built folder.

That's easier to have a doc saying.

git init
percli dac setup
echo "built" >> .gitignore

Less code to maintain and the three lines are self explanatory.

[Nexucis]

I would be in the middle here:

• In case .gitignore exists, then we could append it with the folder built and I think we should add a comment in the .gitignore explaining what is this folder ignored. Like

# folder used to store the result of the command percli dac build
/built

• In other case, I think we shouldn't assume the user is using git or want to use it and so for .gitignore. A user could even have a global .gitignore and so it doesn't need to create one for each project.

• Regarding the documentation, we should just explain what the command is doing. There is no requirement when running the command percli dac setup to use git or to init a repo with git.

Finally, it would be great to be able to change the targeted folder too.