Normalize KFP endpoint URL

[ptitzler]

This PR

• normalizes the KFP endpoint URL by removing trailing /s in methods that process the value instead of relying on the metadata service to perform the normalization
• closes KFP pipeline run link does not work if the KFP API endpoint ends with "/" #1605

The code in the process and export methods already assumed that the URL does not end with /, as seen in https://github.com/elyra-ai/elyra/blob/master/elyra/pipeline/processor_kfp.py#L85, https://github.com/elyra-ai/elyra/blob/master/elyra/pipeline/processor_kfp.py#L231, and https://github.com/elyra-ai/elyra/blob/master/elyra/pipeline/processor_kfp.py#L235

What changes were proposed in this pull request?

How was this pull request tested?

• Created RTC with trailing / in KFP API URL
• Ran pipeline
• Exported pipeline to KFP DSL and ran it

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