Ensure there isn't a trailing slash on the REST URL before we break t…

[dkotter]

Description of the Change

Ensure there isn't a trailing slash on the REST URL before we break that URL into it's various pieces, in our get_site_url_from_rest_url function.

Fixes #585

Benefits

View links for external connections will be correct if that external connection is set up with a trailing slash

Possible Drawbacks

None

Verification Process

1. Created a new external connection with a trailing slash
2. Pushed a post to this connection
3. Verified the View link pointed to the REST URL (i.e. example.com/wp-json/?p=10)
4. Added the fixes here and tested again
5. Verified the View link pointed to the FE URL (i.e. example.com/?p=10)

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

#585

[jeffpaul]

I'll hold off on merging this until we get the auth wizard PR merged in so that we don't create further conflicts on that merge.

[jeffpaul]

The auth wizard PR is merged and it doesn't appear that we've got any merge conflicts here. So @dinhtungdu @dkotter you two 👍 to merge this one in?

[dkotter]

Good on my end