Update LUMI /appl/local support policy

[rkronberg]

Proposed changes

All LUMI support requests, including /appl/local, should now be sent to LUST. CSC support will be notified to resolve /appl/local issues in LUMI RT whenever needed.

https://csc-guide-preview.rahtiapp.fi/origin/lumi-rt-policy-update/support/contact/

Checklist before requesting a review

• [x] I have followed the instructions in the Contributing and Styleguide documents.
• [x] My pull request passes all tests.
• [x] I have included a link to the appropriate preview page (select your branch from the list).