docs: Notes about switching types in session

[neznaika0]

Description
See #9505 (comment)

• Added a clarification.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[neznaika0]

I would add another note about clearing expired sessions. But I don't fully know how to do it.
Example:

For FileHandler, you can clear files using cron.

[michalsn]

I would add another note about clearing expired sessions. But I don't fully know how to do it.

Probably something like this:

0 2 * * * find /path/to/your/project/writable/session -type f -name 'ci_session*' -mmin +1440 -delete

It will delete stale sessions that haven’t been used for more than 24 hours.

• The session path should be set to: Config\Session::$savePath.
• The session name should be set to: Config\Session::$cookieName
• The user running the cron job should have permission to access and delete those session files.

[neznaika0]

• Deleting expired session files

[michalsn]

Looks good. Thanks!

[paulbalandan]

Minor grammar fix.