Remove deprecation warning for local runtime type

[kiersten-stokes]

Fixes #2855

What changes were proposed in this pull request?

Based on some discussion related to #2855, we decided to consider lowercase local equivalent to uppercase LOCAL when checking against runtime types. This PR suppresses the warning message about using (eventually) deprecated runtime type names (kfp, airflow) for the local runtime only. This is the 'path of least resistance' for this issue. If we ever fully remove the ability to query with the lowercase local, we'll probably want the frontend to adjust its API call to use the LOCAL RuntimeProcessorType Enum member.

How was this pull request tested?

Queried the elyra/pipeline/components/{runtime_type} endpoint with local as the runtime_type, and no warning message is shown in the logs. A new test is added to cover this case as well.

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[kevin-bates]

Sorry, but would it be possible to add a handlers test that used local (and reproduces the problem prior to this fix)? If that turns out to be a hassle, I'm okay moving forward, but I think it would be good to have in case we make changes later that wind up side-affecting this PR.

[kevin-bates]

Thanks for adding the test - this LGTM.