Opt-in memory collections' snapshopts

[nicola-corbellini]

Description

Now, saving the vector memory collections' snapshots is optional.
Default behavior is saving the snapshots, but this can be turned off setting SAVE_MEMORY_SNAPSHOTS=false in the .env file.

Related to issue #463

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas

[pieroit]

Sorry for checking this only now... would you mind to make it the opposite?
Opt-in = turned off by default, user activates
Opt-out = turned on by default, use deactivates

[nicola-corbellini]

Yep, done. Default is now false