Reformat the user identity table

What does this MR do and why?

We have reformat the user identity table in the following ways.

• Added two columns: Provider ID and Group
• Use the Pajamas styles for the table
• Add a zero/empty state (no identities) within the table
• Represent the delete and edit actions with icons

Part of #294608 (closed)

Screenshots or screen recordings

Current

Proposed

Implemented

Note:

1. that I added the title Actions to the last column, to make it consistent with other tables (for example the personal access token table):

2. I used dashes - for empty data instead of N/A. N/A is not used anywhere in GitLab and it could be challenging to translate to languages that doesn't have similar abbreviation.
3. I used tertiary default buttons (instead of tertiary danger) for the delete button because the repetition of red icons can be distracting, see also here.

How to set up and validate locally

1. Login as an admin
2. Go to the user identity tab for one user, for example: https://gdk.test:3443/admin/users/randy/identities
3. Create several identities to see the different fields

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.