Improve error message when JDS can't connect to a local TP

[pavlenex]

For JDS a local Template Provider needs to run first otherwise this happens:

2024-01-23T09:21:59.599341Z  INFO jd_server::lib::job_declarator: JD INITIALIZED
thread 'tokio-runtime-worker' panicked at jd-server/src/lib/mempool/mod.rs:60:77:
called `Result::unwrap()` on an `Err` value: JsonRpc(Transport(SocketError(Os { code: 61, kind: ConnectionRefused, message: "Connection refused" })))
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread 'tokio-runtime-worker' panicked at jd-server/src/lib/mempool/mod.rs:75:14:
called `Result::unwrap()` on an `Err` value: JoinError::Panic(Id(10), ...)

We should ensure a better error message is presented to the user. Problem is that JDS can't connect to TP to local TP for a few reasons, and we have no way apparently to know what are these reasons (TP not fully synced, TP down).

Suggested message could be: Unable to connect to TP (possible reasons: not fully synced, down)

[GitGab19]

I would add that another issue is that the JDS mempool is updated every 10 seconds, which is hardcoded here.
The update rate should be configurable by the user.
I'm working on fixing both issues, I will open a PR soon

[GitGab19]

I would add that another issue is that the JDS mempool is updated every 10 seconds, which is hardcoded here. The update rate should be configurable by the user. I'm working on fixing both issues, I will open a PR soon

I fixed them here: #727