update solochain to use #[runtime] (#5772)

# Description

* This is part of [issue
5242](https://github.com/paritytech/polkadot-sdk/issues/5242),
specifically getting solochain to use `#[frame::runtime]`
* Furthermore, reinforced the convention of `Template` instead of
`TemplateModule`


## Integration

* Should be integrated into the `solochain` template and documentation

## Review Notes

* Refactored `solochain` template from
[construct_runtime!](https://paritytech.github.io/polkadot-sdk/master/frame_support/macro.construct_runtime.html)
to
[#[runtime]](https://paritytech.github.io/polkadot-sdk/master/frame_support/attr.runtime.html).
* AFAIU `Template` is our new convention, and preferred over
`TemplateModule`.

# Out of scope

* The
[#[runtime]](https://paritytech.github.io/polkadot-sdk/master/frame_support/attr.runtime.html)
documentation is still very rudimentary, and should ideally be expanded
to explain the macro, both what it does and the input options.
* Furthermore, suggest update
[#[runtime]]...