Add Dockerfile template for Dart projects

[chimon2000]

This pull request adds a Dockerfile template for Dart projects.

Notes

Tested the Dockerfile locally, and I was able to at least get to the point where the protocol buffer contract was failing.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (8a3de51) 1.35% compared to head (ec85b33) 1.35%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #691 +/- ## ===================================== Coverage 1.35% 1.35% ===================================== Files 71 71 Lines 7250 7250 ===================================== Hits 98 98 Misses 7147 7147 Partials 5 5 ``` | [Flag](https://app.codecov.io/gh/nitrictech/cli/pull/691/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nitrictech) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/nitrictech/cli/pull/691/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nitrictech) | `1.35% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nitrictech#carryforward-flags-in-the-pull-request-comment) to find out more.

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[davemooreuws]

Hey @chimon2000 this isn't completely finished (other runtime code needs to be added). We took the dockerfile and put it in this PR: https://github.com/nitrictech/cli/pull/692 , we will add some caching to it in another commit and co-author you.