feat(keyring-controller): add isKeyringNotFoundError

[ccharly]

Explanation

Adding this helper so we can use it in combination with withKeyring, e.g:

try {
  await controller.withKeyring({ type: 'something' }, ({ keyring }) => {
    ...
  });
} catch (error) {
  if (isKeyringNotFoundError(error)) {
    await controller.addNewKeyring('something');
  }
}

// We can retry to use `withKeyring` now.

References

N/A

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them