fix: do not route to plugin when command is invalid

[goldbez]

Description of changes

When commands are deemed invalid by the input-manager, the command is set to "help" but the plugin is not changed. This leads to invalid commands still being routed to non-core plugins, which sometimes results in users being prompted, even after a message showing that the command is invalid is printed. This change stops commands from being routed to plugins by setting the plugin to core. The plugin that executes the help command does not matter, as all plugins yield the same top-level help. See the first photo below for an example of a prompt appearing after an invalid command message and the second photo for the new behavior.

Issue #, if available

#12118

Description of how you validated changes

Checklist

• PR description included
• yarn test passes
• [] Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)
• New AWS SDK calls or CloudFormation actions have been added to relevant test and service IAM policies
• Pull request labels are added

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[aws-eddy]

Excellent fix! Are we capturing/validating this behavior anywhere in e2e tests?

[codecov-commenter]

Codecov Report

Merging #12132 (562e192) into dev (984c0f8) will decrease coverage by 3.14%.
The diff coverage is 56.28%.

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@@            Coverage Diff             @@
##              dev   #12132      +/-   ##
==========================================
- Coverage   49.45%   46.32%   -3.14%     
==========================================
  Files         692      821     +129     
  Lines       33424    37587    +4163     
  Branches     6840     7643     +803     
==========================================
+ Hits        16529    17411     +882     
- Misses      15370    18514    +3144     
- Partials     1525     1662     +137     

Impacted Files	Coverage Δ
...sync-simulator/src/data-loader/opensearch/index.ts	45.45% <0.00%> (ø)
...s/amplify-appsync-simulator/src/type-definition.ts	100.00% <ø> (ø)
...sync-simulator/src/velocity/util/dynamodb-utils.ts	6.55% <0.00%> (ø)
...y-appsync-simulator/src/velocity/util/map-utils.ts	10.00% <ø> (ø)
...tor/src/velocity/util/transform/dynamodb-filter.ts	4.93% <0.00%> (ø)
...ync-simulator/src/velocity/util/transform/index.ts	21.05% <0.00%> (ø)
...appsync-simulator/src/velocity/value-mapper/map.ts	86.88% <ø> (ø)
...ackages/amplify-category-auth/src/commands/auth.ts	0.00% <0.00%> (ø)
...es/amplify-category-auth/src/commands/auth/help.ts	0.00% <0.00%> (ø)
.../amplify-category-auth/src/commands/auth/import.ts	0.00% <0.00%> (ø)
... and 539 more

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