docs(guides): add vacuum process

docs/guides/vacuum.md

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+---
+sidebar_position: 500
+---
+
+# Vacumm (Auto clean expired packages)
+
+aqua >= [v2.43.0](https://github.com/aquaproj/aqua/releases/tag/v2.43.0)
+
+Vacuum is a managed mode of aqua which permits the removal of packages not used for a specified time.
+
+## To enable it
+
+Vacuum is disabled by default. To enable it, you need to set the `AQUA_VACUUM_DAYS` environment variable to an integer greater than 0, which represents the number of days a package should not be used to be considered as unused.
+
+:::caution
+If you want to use this feature, we recommend setting this variable in a way that you use it with each aqua command. (~/.bashrc, ~/.zshrc, ~/.rc.d, etc.)
+:::
+
+## Workflow
+
+When vacuum is enabled, each time a command like `aqua install` or `aqua exec` (or any command executed through aqua) is executed, aqua will add (or update) an entry in a bbolt database with corresponding information and a timestamp of the last usage.
+
+When `aqua vacuum run` is executed, aqua will check all entries in the database and remove packages that have not been used for more than `AQUA_VACUUM_DAYS` days.
+
+Every expired package will be removed from the `pkgs` directory and from the database.
+
+## Commands
+
+```console
+$ aqua vacuum show [--expired] # List all packages managed by vacuum [--expired show only expired packages]
+```
+
+```console
+$ aqua vacuum run # Run the vacuum process
+```
+
+## Limitation
+
+:::caution
+Every package installed before the activation of vacuum will not be managed by vacuum. So to start with a clean process, we recommend launching aqua rm --all the first time.
+:::