msa: removed callback from add_key

[aramikm]

Goal

The goal of this PR is to simplify add_key by removing on_success callback.

Closes #2502

Checklist

• Updated Unit Tests
• Spec version incremented?

[codecov]

Codecov Report

❌ Patch coverage is 95.83333% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pallets/msa/src/lib.rs	95.83%	1 Missing ⚠️

Files with missing lines	Coverage Δ
pallets/msa/src/types.rs	100.00% <ø> (ø)
pallets/msa/src/lib.rs	92.47% <95.83%> (-0.17%)	⬇️

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[JoeCap08055]

Nice cleanup/simplification!

[enddynayn]

👍 Nice!

[mattheworris]

🚢 it!