Allow for trailing slash in supabaseUrl

[adam-beck]

What kind of change does this PR introduce?

Feature

What is the current behavior?

A trailing slash in the supabaseUrl causes duplication in the final URL

What is the new behavior?

A trailing slash is removed from the supabaseUrl so the created URL does not contain duplicates

Additional context

• The regex only accounts for a single \.
• Another option would be to update the docs, but this improves DX as there is no need to worry about if a slash should be appended to the URL or not
• fixes When SUPABASE_URL has a trailing slash, authentication with the Auth component does not work #261