[FX-580] Add trailing slash to all requests

[dleis612]

What

Add trailing slashes to all http requests that were missing them.

Test Plan

I tested this locally by running through a checkout and looking at the datadog logs.

[djoksimo]

doing addPathSegment("") is not clear that we're adding a trailing slash.

Would doing something like adding this extension work:

// in `OkHttpClientBuilder.kt` or new file: `HttpUrlExtensions.kt`
fun HttpUrl.Builder.addTrailingSlash(): HttpUrl.Builder {
    return this.addPathSegment("")
}

// in encryption key service

 return httpUrl
            .newBuilder()
            .addPathSegment(ForageConstants.PathSegment.ISO_SERVER)
            .addPathSegment(ForageConstants.PathSegment.ENCRYPTION_ALIAS)
            .addTrailingSlash()
            .build()

alternatively, can you add comments for each call to addPathSegment("")

[dleis612]

This is a pretty cool optimization I didn't know was possible :)

[dleis612]

ed1f578