Implement RegeneratePersonalAccessToken RPC

[laushinka]

A user can re-generate their token. This action performs the following:

• For a given Token ID, create a new Personal Access Token (similar to the Create flow) and persist the new token under the existing Token ID (update).
• Re-generating a token requires expiry of the regenerated token to be set, and must therefore also update the Expiry Time
• When regenerating, you must ensure the token being updated belongs to the user from the request

Acceptance Criteria:

• Implement RegeneratePersonalAccessToken in https://github.com/gitpod-io/gitpod/blob/main/components/public-api-server/pkg/apiv1/tokens.go#L106
• Ensure good test coverage