Add authentication and authorization checks to unsecured server actions

[gabestein]

Motivation

A bunch of server actions atm are not secured at all. While easy to forget, these things are basically API endpoints, and atm for a lot of actions just about anyone can access them.

Requirements

• Add authentication checks to all server actions
• Move exports of non-client called functions out of files with "use server"
• Add authorization checks to relevant server actions
• Sends authorization error with generic "You are not authorized to perform this action." message

Acceptance Criteria

Missing authentication & Authorization checks

• [ ] All the actions for the formbuilder: https://github.com/pubpub/platform/blob/605cb02e1bb2cdb12ce13fbd6991797dd8e9c78e/core/app/components/FormBuilder/actions.ts#L15-L16

• [ ] All fields server actions https://github.com/pubpub/platform/blob/bd08a370f26b47b434ac5cc3fe7adb815b9d68e0/core/app/c/%5BcommunitySlug%5D/fields/actions.ts#L1-L73

• [ ] The move and assign actions https://github.com/pubpub/platform/blob/e8baa1b18ce0777f3831e5659297701c91f67ab5/core/app/c/%5BcommunitySlug%5D/stages/components/lib/actions.ts#L1-L50

• [ ] All the stages/manage actions https://github.com/pubpub/platform/blob/e8baa1b18ce0777f3831e5659297701c91f67ab5/core/app/c/%5BcommunitySlug%5D/stages/manage/actions.ts#L1-L296

• [ ] All the types actions https://github.com/pubpub/platform/blob/180712d166b9dd231fe6ef5958fd30701690dfa7/core/app/c/%5BcommunitySlug%5D/types/actions.ts#L1-L78

• [ ] The _updatePub function should be moved to lib/server/pub.ts. Currently it's exported and therefore a server action https://github.com/pubpub/platform/blob/b9914b22cc7eeb55f9986cafaf6bf9f42789b4ac/core/app/components/pubs/PubEditor/actions.ts#L46-L56

Missing authorization checks (in addition to the above)

(can't find that very quickly, should probably be rethought anyway once we have our new permissions model in place)