core-components: add lint rule to avoid circular imports

[BethGriggs]

Hey, I just made a Pull Request!

Trying to be proactive to avoid issues like https://github.com/backstage/backstage/pull/24511, so figured I'd propose adding a lint rule to packages/core-components. Here's what the lint output would have been:

$ yarn lint
Lint failed in packages/core-components:
✘  http://eslint.org/docs/rules/no-restricted-imports

     '@backstage/core-components' import is restricted from being used.  To avoid circular dependencies, use relative paths to import '@backstage/core-components' from its subdirectories

     src/layout/HeaderTabs/HeaderTabs.tsx:21:1
     19 | import Tabs from '@material-ui/core/Tabs';
     20 | import React, { useCallback, useEffect, useState } from 'react';
   > 21 | import { Link } from '@backstage/core-components';
        | ^
     22 | 
✘ 1 problem (1 error, 0 warnings)

:heavy_check_mark: Checklist

• [ ] A changeset describing the change and affected packages. (more info)
• [ ] Added or updated documentation
• [x] Tests for new functionality and regression tests for bug fixes
• [ ] Screenshots attached (for UI changes)
• [x] All your commits have a Signed-off-by line in the message. (more info)

[github-actions[bot]]

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