support akeyless secrets

What does this MR do?

Adding support to authenticate and fetch secrets from akeyless

Why was this MR needed?

With this feature we will be adding a new CI configuration as such:

job:
  id_tokens:
    AKEYLESS_JWT:
      aud: 'https://gitlab.com'
  secrets:
    DATABASE_PASSWORD:
      token: $AKEYLESS_JWT
      akeyless:
        name: 'my-project-secret'

With this configuration, the job would have the secret retrieved from Akeyless Secret stored in the build variable DATABASE_PASSWORD.

The implementation of the CI config in Rails is in this MR: gitlab!147283 (closed)

What's the best way to test this MR?

1. Log in to Akeyless https://console.akeyless.io/
2. Create a new static secret: https://docs.akeyless.io/docs/static-secrets
3. Create authenticate method of type OAuth2.0/JWT: https://docs.akeyless.io/docs/oauth20jwt
4. Create a Role to the auth method you created to be able to access the secret: https://docs.akeyless.io/docs/rbac
5. Set up a GDK environment with this gitlab-runner and gitlab gitlab!147283 (closed)
6. Use the YAML example I wrote in the description and update the name and the AKEYLESS_ACCESS_ID variable in the CI/CD.
7. Run the pipeline and see that you got the secret in the build variable DATABASE_PASSWORD.

What are the relevant issue numbers?

Related to gitlab#443305 (closed)