lint: specify image version (#4)

## The Issue

Currently, we default to `latest` for the Netdata docker image. This
leads to instability and potential fails.

<!-- Provide a brief description of the issue. -->

## How This PR Solves The Issue

This PR sets a specific version, `v2.8.2`. 

<!-- Describe the key change(s) in this PR that address the issue above.
-->

## Manual Testing Instructions

<!-- If this PR changes logic, consider adding additional steps or
context to the instructions below. -->

```bash
ddev add-on get https://github.com/tyler36/ddev-netdata/tarball/refs/pull/REPLACE_ME_WITH_THIS_PR_NUMBER/head
ddev restart
```

## Automated Testing Overview

<!-- Please describe the tests introduced by this PR, or explain why no
tests are needed. -->

## Release/Deployment Notes

<!-- Does this affect anything else or have ramifications for other
code? Does anything have to be done on deployment? -->

feat: Add Netdata service (#1)

This PR is the initial release of the addon.

It adds the NetData service to a DDEV project and a helper command `ddev
netdata`) to launch the dashboard.