Ideas to improve organization of variants in code and playground

[mmabrouk]

• One feedback we have received from early users is that they find it challenging to remember which variant in the code corresponds to which variant in the playground.
• This confusion arises because the script name is not always the same as the variant name.
• Additionally, when a variant is created in the playground by forking another variant, the link to the original variant is lost.

To address these issues, we propose the following changes:

1. Modify the "agenta variant serve" feature to disallow users to specify a custom name for the variant, instead we automatically use the script name as the variant name.
2. With this modification, users can use the agenta variant serve command as follows: agenta variant serve filename.py which will create a variant named filename.
3. When a variant is forked in the user interface, it will be named variant.forkname instead of newvariantname. This naming convention will help users identify all the variants that were created from one specific piece of code. All variants based on a certain script will be called scriptname.something