feat(admin): get admin by id, unselect admin password field

[kon14]

This PR introduces a new administrative route for retrieving unique admin users by id (/admins/:id).
Passing in me as the admin id returns the authenticated user performing the request.

I also removed password from Admin schema's default field selection, explicitly selecting it where required and performed some minor cleanups across the place.

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other (please describe)

Does this PR introduce a breaking change?

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the main branch
• When resolving a specific issue, it's referenced in the PR's description (e.g. fix #xxx, where "xxx" is the issue number)

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature

Other information: