feat: add extraManifest

[sinux-l5d]

What this PR does / why we need it:

This PR adds a extraManifest key. It allows arbitrary deployment of a Kubernetes manifest within the same Helm release.

In our case, we deploy an extra Secret that uses helm-secrets.

Which issue this PR fixes

• fixes [zabbix-community/zabbix] extraDeploy section #119

Special notes for your reviewer:

We've discussed in the issue above about "add[ing] and test[ing] all occurrences of extra parameters like extraEnv". However I don't see the connection between extraEnv and extraManifest: the latter should be added as-is in the release, without modification from other extra parameters.

Checklist

• DCO signed
• Chart Version bumped
• Variables are documented in the README.md

[fibbs]

Thanks for this contribution! I will test it!
I feel like a dot-dot-release upgrade would be enough for this PR? So, not raising Chart version to 6.1.0 but to 6.0.2 instead? (.2 because of #123 raising to 6.0.1). @aeciopires what do you think?

[aeciopires]

Hi @sinux-l5d!

Thanks for your contribution. I will review your PR.

Hi @fibbs!

The goal of this PR is to add a new "feature" to the chart, it is not a hotfix. I agree with 6.1.0.

But the publishing of the helm chart is associated with the manually created tag. Using this approach, I can accumulate many PRs and publish all the changes together. That is why I did not add helm docs to the pipeline to avoid conflicts. I had a lot of problems with this last year.

So, during the process of publishing a new release, I evaluate all the changes from the PRs that I will publish, choose the appropriate version number and then publish them in one package...

The explanation for this is that last year I was very busy at work, so several PRs accumulated throughout the year and I published them all in one batch release.

Another reason is that some people who opened the PR were not responding quickly when I had free time (which is normal because everyone's schedule is asynchronous even depending on their interest and free time).

[sinux-l5d]

It should be okay now @aeciopires :)

EDIT: let me know if you need me to squash

[aeciopires]

Thanks @sinux-l5d!

It`s ok to me!

@fibbs I will let merge with you to solved possible conflict in code with other PRs