Seek for Websocket Consumer API

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Motivation

I would like to create a web client dashboard that would get the messages for some topic over the last hour or so and display it.

### Solution

Add the "seek" feature for the Websocket Consumer API to access older messages by timestamp.

### Alternatives

I usually use Rust to build web apps, but the [pulsar-rs](https://github.com/streamnative/pulsar-rs) project doesn't support WASM, although it supports `seek`.

### Anything else?

I'm working on my first project using Pulsar, so apologies if I missed something obvious.
I'm not confident I could make a PR unless the implementation is somewhat trivial.

I'm referring to this missing feature from [this matrix](https://docs.google.com/spreadsheets/d/1YHYTkIXR8-Ql103u-IMI18TXLlGStK8uJjDsOOA0T20), currently in cell N69.

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start with the Websocket Consumer API and the requested timestamp-based access to older messages. The issue names no files or tests, so first identify the relevant entry point and define the API behavior. Done means a web client can seek to a timestamp and receive older messages from the topic.

Written by the indexing model from the issue text.