Allow user to have multiple keypairs

[kyujin-cho]

Main idea

Our current user authentication architecture allows user to have only one keypair at once. Let's extend this architecture so that we can let users create multiple keypairs for a single account.

We can split this issue to smaller chunks, like:

• manager: let main keypair (the one generated when creating user) as a "default keypair" to user, and use it as a login credential when logging in to Backend.AI WebUI with session mode

• manager: add API to support arbitrary keypair creation/removal* _{limit additional keypairs not to have resource limits bigger than default keypair}

• feature: Materialization of the "main" keypair concept #1761 now enforces user-wide resource constraints via the main keypair's resource policy

• Migrate and merge the keypair resource policy into the user resource policy

• manager: search for usages of keypair in manager code, and if the structure isn't suitable for multiple keypair situation, update it

• webui: create corresponding UI for keypair creation/removal

  Side-effects of keypair-based resource policy

• What users wanted* lablup/giftbox#191

• lablup/giftbox#10

• Bulk-updating project-wise user (=keypair) resource policies with a filtered view of projects that the keypair's owner is a member of.

• We implemented feat: Let the queryfilter-minilang engine to fetch multiple rows from joined tables #1022 to add the "projects" column to the view of "keypairs" in the control panel.

• Side-effects that happened* User who doesn't have a project cannot log in. #1625

• 23.09: Polish the current multiple keypair scheme
  {code:[tasklist]}

Tasks

• fix: Unable to login and missing keypairs when a user does not have any project #1360
• feature: Materialization of the "main" keypair concept #1761
• fix: Update fixtures to include setting main keypairs #1785
• fix: Regression of purging user due to fkey constraint of main_access_key #1775

{code}

• 24.03: Ultimately we need to deprecate per-keypair resource policy and keep per-user resource policy only.* fix: Deprecates querying projects from KeyPair query #1779
• Split the users table into identities and user_profiles #1783