feat: allow api version override

[viceice]

• Allow api version override
• Simply api version check
• Add some docs

closes #145

[ekeih]

Hi, thanks for implementing this override @viceice! I just wanted to use helm template with this chart and was very happy to see that this change just got merged three hours ago 🙂
If I am not mistaken this release is not available at https://docs.renovatebot.com/helm-charts, is this on purpose? 🤔 (Maybe some automation didn't like the renovate-25.64.1+1 instead of renovate-25.64.2? 😄)

[ekeih]

https://github.com/renovatebot/helm-charts/releases/tag/renovate-25.65.0 seems to be publised to the helm repository now. Not sure if that was in response to this comment or not, but either way your work is greatly appreciated and the release seems to work! Thanks 🙂

[viceice]

We currently follow the main renovate versions, so i can only publish the chart with a sub version +1 but the chart-releaser tool won't publish it to the gh-pages 😕

Maybe some knows better tooling for automated helm chart releasing. Currently all we need to do is to wait for next automatic renovate release, which will be multiple times a day

[viceice]

see also #54

[ekeih]

I see, thanks for the explanation @viceice! Normally, waiting for the next automated release should be fine, yesterday I was just trying to use it too fast :)