Able to help? Yes.
Move moodledata to the largest partition via mv command. Update moodle's config.php to point to new location.
You might use du -h on moodledata to assure there is enough space on largest partition before moving.
Removing all files in moodledata/sessions/ would be a temporary fix true, but nice to know should you have need of a quick fix.
Since it appears you have a 'tangled' system (Azure/Ubuntu guest OS/ and bitnami (entire stack) suggest your first resource for issues might need to be Bitnami's forums.
https://community.bitnami.com/
Bitnami might have provided an easy install of entire stack but maintenance etc. is all command line via Bitnami's .sh commands - from what I read..
Also, you've posted in Developer Forum here ... this really isn't a developer question ... next time try to pick an appropriate forum for the issue ... General Help if you can't decide.
'SoS', Ken