Fix optional route bug

[JulienRobitaille]

Optional routes are not working anymore because the ? gets escaped by the change introduced in: f12e237

This code handle that scenario by looking at the last character of the path before doing the escape.
When the last character is a ? it will do the escape on the path and prevent the escape of the needed ?.

I've added test to verify that optional routes are now working alongside the regexp meta character in path changes.

If you feel this change is not welcome, please close the PR but since it was a "very clearly well identified bug" It felt appropriate.

This PR fixes #1008

[tomchristie]

So, you probably don't want an optional trailing slash. Starlette will handle trailing slash redirects appropriately for you, so you can add either /optional-path/ or /optional-path depending on which you want the canonical form to be, and you'll automatically get redirect behaviour from the other variant.

[evanlurvey]

I personally like this slash patcher more. Doesn't create dup docs or dup routes just fixes the regex.

def slash_patcher(app: FastAPI):
    app.router.redirect_slashes = False
    for r in app.routes:
        if r.path_regex.pattern.endswith("/$"):
            r.path_regex = re.compile(r.path_regex.pattern.replace("/$", "/?$"))
        else:
            r.path_regex = re.compile(r.path_regex.pattern.replace("$", "/?$"))