Follow-up Adjust approvals table - table header translations

What does this MR do and why?

data-label attributes for the collapsible table were using strings, while table headers in the Project settings and MR edit apps were bound to constants. This could have resulted in changed copy for the table that would not be reflected on the mobile screens.

I've moved the definition of the headers to constants.js file, because they are used across two different apps and additionally in one component shared between them.

Binding the headers to the body of the table component allows using them in data-label of each <td> element.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Choose a project and go to Settings > Merge request
2. Scroll down to Merge request approvals.
3. View the table in desktop and mobile mode. Table headers should be the same.
4. To test changes in MR edit view select an existing MR and click Edit button
5. Scroll down, between Reviewers and Milestone, expand Approval rules.
6. View the table in desktop and mobile mode. Table headers should be the same.

Related to #439889 (closed)