Create a resource for the account admin user

[micahlee]

Desired Outcome

The desired outcome of this PR is for the account admin to list its grants.

Implemented Changes

This PR adds the account admin as a Resource in the Conjur database so that all existing authorization controls apply to it as well.

Connected Issue/Story

Follow up to #2755

Definition of Done

At least 1 todo must be completed in the sections below for the PR to be
merged.

Changelog

• The CHANGELOG has been updated, or
• This PR does not include user-facing changes and doesn't require a
  CHANGELOG update

Test coverage

• This PR includes new unit and integration tests to go with the code
  changes, or
• The changes in this PR do not require tests

Documentation

• Docs (e.g. READMEs) were updated in this PR
• A follow-up issue to update official docs has been filed here: [insert issue ID]
• This PR does not require updating any documentation

Behavior

• This PR changes product behavior and has been reviewed by a PO, or
• These changes are part of a larger initiative that will be reviewed later, or
• No behavior was changed with this PR

Security

• Security architect has reviewed the changes in this PR,
• These changes are part of a larger initiative with a separate security review, or
• There are no security aspects to these changes

[imheresamir]

LGTM, thanks!

[codeclimate]

Code Climate has analyzed commit 26e689d and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 90.3% (-1.6% change).

View more on Code Climate.