Change type of `invenio.extra_env_from_secret`

[lindhe]

Description

This change fixes a typo for the default value (and importantly: type) of the invenio.extra_env_from_secret value.

Before this change, I got the following warning when setting invenio.extra_env_from_secret:

coalesce.go:286: warning: cannot overwrite table with non table for invenio.invenio.extra_env_from_secret (map[])

This was because the default value of invenio.extra_env_from_secret was {} (the empty object) while it is clearly used as a list:

https://github.com/inveniosoftware/helm-invenio/blob/eb6544fdeb7e762972db1dae26f848c2f2e4c029/charts/invenio/templates/web-deployment.yaml#L83-L89

https://github.com/inveniosoftware/helm-invenio/blob/eb6544fdeb7e762972db1dae26f848c2f2e4c029/charts/invenio/templates/worker-deployment.yaml#L87-L93

So when setting invenio.extra_env_from_secret to a list instead of an object, Helm gets nervous. This change fixes that.

I've also added an example comment to show what the structure of each list item should be.

In the long term, I believe a more overarching change as discussed in #117 is better. My change here is just a quick bug fix.

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• [x] I'm aware of the code of conduct.
• [x] I've created logical separate commits and followed the commit message format.
• [ ] I've added relevant test cases.
• [ ] I've added relevant documentation.
• [ ] I've marked translation strings (for relevant code).
• [ ] I've followed the CSS/JS and React guidelines (for relevant code).
• [ ] I've followed the web accessibility guidelines (for relevant code).
• [ ] I've followed the user interface guidelines (for relevant code).
• [ ] I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• [x] I've NOT included third-party code (copy/pasted source code or new dependencies).

Third-party code

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[lindhe]

It seems like this did not fix the warning. Let me try some more before merge.

[lindhe]

False alarm! It did fix the bug, I just tested on the wrong branch. 🙃