Add another issue template

[athowes]

In working on epidist I am often copy pasting in this issue template. I find that a more verbose template (as a nudge) is probably useful. Could we add something like this to the possible epinowcast issue templates?

This template should be used as an outline. It may not be necessary to fill out every section. Delete this block of text and fill in anything in brackets. See this [example issue](https://github.com/cdcent/cfa-nnh-pipelines/issues/107) for inspiration.

## Goal

[1-3 sentence summary of the issue or feature request. E.g. "We want to be able to ..."]

## Context

[Short paragraph describing how the issue arose and constraints imposed by the existing code architecture]

## Required features

- [Describe each thing you need the code to do to achieve the goal]
- [Example 1: Use a config to set input and output paths]
- [Example 2: Read in some-dataset and output some-transformed-dataset]
- etc...

## Specifications
[A checklist to keep track of details for each feature. At least one specification per feature is recommended. Edit the example below:]

- [ ] EX2: A function that reads data from the `some-api` API and returns the dataset
- [ ] EX2: Another function that inputs the dataset, performs $x$ transform, and outputs $y$
- [ ] EX1: A script that runs the workflow from a config
- [ ] All functions should follow R package conventions with blah, blah, blah
- [ ] The workflow should run in the VAP from `directory`
- [ ] All functions should have associated unit tests
- [ ] etc. etc. 

## Out of scope

- [Things out of scope from this issue/PR]

## Related documents

- [Link to related scripts, functions, issues, PRs, conversations, datasets, etc.]

[athowes]

@seabbs @pearsonca what do you think?

(Tagging you as contribuitors to this repo, feel free to tag others if you think their input useful etc.)