feat: add updater_tools library

[bryanoltman]

Description

Adds a updater_tools library. This is just the output of very_good create dart_package updater_tools --desc "Tools to create artifacts used by the Updater" with some irrelevant files removed. Because the output of this tool is directly tied to the version of updater, it is being moved here from shorebird_tools in https://github.com/shorebirdtech/flutter/tree/shorebird/dev/packages/shorebird_tools.

Type of Change

• [x] ✨ New feature (non-breaking change which adds functionality)
• [ ] 🛠️ Bug fix (non-breaking change which fixes an issue)
• [ ] ❌ Breaking change (fix or feature that would cause existing functionality to change)
• [ ] 🧹 Code refactor
• [ ] ✅ Build configuration change
• [ ] 📝 Documentation
• [ ] 🗑️ Chore

[codecov[bot]]

Codecov Report

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

Project coverage is 95.98%. Comparing base (d309317) to head (8d0152b).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #162 +/- ## ======================================= Coverage 95.98% 95.98% ======================================= Files 20 22 +2 Lines 2962 2964 +2 ======================================= + Hits 2843 2845 +2 Misses 119 119 ``` | [Flag](https://app.codecov.io/gh/shorebirdtech/updater/pull/162/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=shorebirdtech) | Coverage Δ | | |---|---|---| | [shorebird_code_push](https://app.codecov.io/gh/shorebirdtech/updater/pull/162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=shorebirdtech) | `100.00% <ø> (ø)` | | | [updater_tools](https://app.codecov.io/gh/shorebirdtech/updater/pull/162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=shorebirdtech) | `100.00% <100.00%> (?)` | | 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=shorebirdtech#carryforward-flags-in-the-pull-request-comment) to find out more.

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[bryanoltman]

Might be better named "updater_tools" or similar? Not sure how broad we want this to be.

[felangel]

Might be better named "updater_tools" or similar? Not sure how broad we want this to be.

I slightly prefer updater_tools since this will likely expand over time