FIO-9918 Removed potential trailing slashes in baseURL

[antonSoftensity]

Link to Jira Ticket

https://formio.atlassian.net/browse/FIO-9918

Description

Removed trailing slashes from setBaseUrl, which caused incorrect requests in some cases. Switching requests to URL object was attempted, but it created a lot more issues.

Breaking Changes / Backwards Compatibility

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Checklist:

• I have completed the above PR template
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• My changes include tests that prove my fix is effective (or that my feature works as intended)
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[brendanbond]

Can we do something besides a brittle regex test here? I'd probably reach for new URL in this case to create a deterministic URL every time.

Also, please don't forget tests!

[johnformio]

@antonSoftensity I know you said using the URL object created more object, but I think we should try again. I would start with changing the type of any url parameter to be URL and make sure we are joining the parts to the URL or creating new ones. For example, this creates a valid URL:

const URL = new URL('/abc', 'https://example.com/')

it's just a larger refactor this way, but way safer in the long run