enhancement(refactor)!: Refactor policy Admin API endpoints

[oguzhand95]

Description

Fixes #487

Checklist

• The PR title has the correct prefix
• PR is linked to the corresponding issue
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[charithe]

I think that instead of the FQN, we should let the human readable identifier be the tuple (kind, name, version) which can be represented as a dot separated string (resource.leave_request.default). That shields the users from being exposed to internal implementation details and allow them to work with the concrete data they deal with in the policy files.

Also, I believe the cerbosctl commands need to be updated to handle this change as well. I think we are now losing the ability to filter and sort policies by fields.

[oguzhand95]

@charithe
The table of support for concatenation using || and CONCAT() look like this;

SQLite MySQL PostgresSQL
|   -   |   +   |   +   | CONCAT()
|   +   |   -   |   +   | ||

MySQL documentation suggests executing the following makes MySQL recognize || as concatenation operator. (By default, MySQL treats || as OR.)
SET sql_mode = 'PIPES_AS_CONCAT';

Let's discuss whether this could be an option or not.
One other option may be using goqu to handle the case.

[charithe]

It's a shame that MySQL doesn't conform to ANSI SQL. We'll have to figure out a way to generate the correct CONCAT SQL based on the database dialect. Goqu should have a way of doing that but it's not very obvious. I'll do a bit more digging and discuss the options with you.

[charithe]

LGTM 👍🏽 Just a couple of small nits to address.
Will do a bit of testing tomorrow morning and we can merge this afterwards.

[charithe]

LGTM 👍🏽