replacePrefixMatch broken in main

*Description*:
>What issue is being seen? Describe what should be happening instead of
the bug, for example: Envoy should not crash, the expected value isn't
returned, etc.

with envoy gateway 1.1 I was using following spec

```
- type: URLRewrite
urlRewrite:
path:
type: ReplacePrefixMatch
replacePrefixMatch: /docs/
```

So my goal is to add `/docs/` prefix to all url paths. So it will be modified like `/docs/`.

With latest main the request path was modified only `/docs` (NOTE! missing last slash)

However, with latest main it will not add the ending slash anymore. I was forced to use

```
- type: URLRewrite
urlRewrite:
path:
type: ReplacePrefixMatch
replacePrefixMatch: /docs//
```

to get same behaviour working.

*Repro steps*:
> Include sample requests, environment, etc. All data and inputs
required to reproduce the bug.

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sharing.

*Environment*:
>Include the environment like gateway version, envoy version and so on.

eg 1.1 (envoy 1.31) and main (with envoy distroless-devel)

*Logs*:
>Include the access logs and the Envoy logs.