Introduce API Tokens

[cwperks]

Description

This PR creates a new capability in the security plugin where users can issue tokens and associate permissions directly with the token.

Currently this is limited to security admins.

What is novel about this PR is that we can associated permissions directly with the token instead of OBO tokens which contain a claim with the user's roles that the OBO authenticator uses for authz. With API Tokens an admin can request that the token is scoped down from their own permissions to give the token exactly the permissions it needs. For instance, if the admin only wants the token to have search permissions on a single index, then that can be configured and the token will be unable to perform any other action.

This is a key building block to be able to deprecate and replace Roles Injection which is the current practice for how plugins ensure that tasks or jobs that run asynchronously run with the same restrictions as the user that created the job. Instead, I envision that we require users to issue tokens scoped to exactly the needs for the job to ensure the job runs with only the permissions it needs and no more (principal of least privilege)

• Category (Enhancement, New feature, Bug fix, Test fix, Refactoring, Maintenance, Documentation)

Enhancement

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• Commits are signed per the DCO using --signoff

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