Make versions in chart explicit

[KodrAus]

This PR makes the versioning of the chart explicit, so we'll update it to line up with GitHub releases. The version of the chart isn't necessarily exactly the same as datalust/seq, but kept in-sync enough that users should be able to apply the {year}.{minor} versioning scheme to any Seq-related projects they interact with.

The process for making a release would then be:

1. Merge some changes to the chart definition
2. Create a release PR that updates the build number appropriately
3. After merging the release PR, create a GitHub release with the same version

New major/minor Seq versions will run similarly, except they'll likely only need to update the versions in the Chart.yaml file.

[KodrAus]

Error: Chart.yaml: appVersion should be of type string but it's of type float64

🙄