Fix keystore CLI embedding

[connorwstein]

2 problems trying to embed the keystore CLI in another CLI https://github.com/smartcontractkit/chainlink-ccv/pull/514/files#diff-1eaf102507dc7ff7fa1eb95081337e11c03f57da601dd793f21763033499c324R37:

• The cmd.Root() call in loadKeystore should be a cmd.Parent() otherwise when embedded it will resolve to the higher level command, when really it should be the immediate parent.
• (cosmetic) The name of the root command should be "keystore" so that when embedded it can be used like ./myservice keystore list

[github-actions]

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[github-actions]

✅ API Diff Results - No breaking changes

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