We had concerns about the cached values on Redis with the previous two
releases strategy:

First release (this commit):
  - Create new encrypted fields in the database.
  - Start populating new encrypted fields, read the encrypted fields or
    fallback to the plaintext fields.
  - Backfill the data removing the plaintext fields to the encrypted
    fields.
Second release:
  - Remove the virtual attribute (created in step 2).
  - Drop plaintext columns from the database (empty columns after
    step 3).

We end up with a better strategy only using migration scripts in one
release:
  - Pre-deployment migration: Add columns required for storing encrypted
    values.
  - Pre-deployment migration: Store the encrypted values in the new
    columns.
  - Post-deployment migration: Remove the old unencrypted columns

When referencing cross-namespace labels, we append the namespace name
to the rendered label.

This MR escapes the name to prevent XSS attacks.

Disabled features are ignored as they are grey areas

Some feature allows GUEST to access only if project is not private.
This method returns access level when targeting private projects.

Guest are blocked to certain feature when project is private,
therefore the scope would filter additionally with REPORTER level.

Remove impossible cases due to private project's features can only be
private or disabled.

Fix spec due to sidekiq indexing not triggered.

Update guest use cases: some features has additional constraint that
"Guest users are able to perform action on public/internal projects,
but not private ones."