AppendPaths appends the tailDir to the `path` of the passed in uris.

JoinURLPath forces a relative path join by removing any leading slash, then re-prepending it later.

NewMemoryBackedQuotaPool creates a MemoryBackedQuotaPool from a parent monitor m with a limit.

RedactURIForErrorMessage redacts any storage secrets before returning a URI which is safe to return to the client in an error message.

URLSeparator represents the standard separator used in backup URLs.

MemoryBackedQuotaPool is an IntPool backed up by a memory monitor.