Feature: custom queries

[monofox]

This commit enables function to define custom queries within configuration file or by environment variables.

Its not scope of this commit to define custom queries on-the-fly on the ui.

Closes #24

[monofox]

I had to put it back to draft.
During testing in my own dev-test i stumbled across issues with the docker i did not faced locally.

For example:

web-1     |    0: __rustc::rust_begin_unwind
web-1     |    1: core::panicking::panic_fmt
web-1     |    2: core::result::unwrap_failed
web-1     |    3: <taskwarrior_web::core::app::AppState as core::default::Default>::default
web-1     |    4: taskwarrior_web::main::{{closure}}
web-1     |    5: tokio::runtime::park::CachedParkThread::block_on
web-1     |    6: tokio::runtime::context::runtime::enter_runtime
web-1     |    7: tokio::runtime::runtime::Runtime::block_on
web-1     |    8: taskwarrior_web::main
web-1     | note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
web-1     |
web-1     | thread 'main' panicked at src/core/app.rs:78:51:
web-1     | Config folder cannot be created.: Os { code: 13, kind: PermissionDenied, message: "Permission denied" }
web-1     | stack backtrace:
web-1     |    0: __rustc::rust_begin_unwind
web-1     |    1: core::panicking::panic_fmt
web-1     |    2: core::result::unwrap_failed
web-1     |    3: <taskwarrior_web::core::app::AppState as core::default::Default>::default
web-1     |    4: taskwarrior_web::main::{{closure}}
web-1     |    5: tokio::runtime::park::CachedParkThread::block_on
web-1     |    6: tokio::runtime::context::runtime::enter_runtime
web-1     |    7: tokio::runtime::runtime::Runtime::block_on
web-1     |    8: taskwarrior_web::main
web-1     | note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Other errors included issues with permission when creating the .config folder (i did not had it mounted).

[monofox]

Sorry for the confusion, now I'm ready.