Unit test to confirm that the mysqlctl rice box is current

[rohit-nayak-ps]

Description

We recently had an issue where the init_db.sql has been updated but the corresponding rice box was not updated. (rice box reference: https://github.com/GeertJohan/go.rice)

All files in the config directory are part of this rice box. This PR adds a unit test to compare these files on disk with that embedded in the rice box.

The other rice-box usage is around the old vtctld UI and embedded vitess binaries, those are not tested for.

[mattlord]

Related to this: #10094

[github-actions]

Review Checklist

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Bug fixes

• There should be at least one unit or end-to-end test.
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New/Existing features

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Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• vtctl command output order should be stable and awk-able.

[mattlord]

Nice! I like it ❤️