add(ci): GitHub workflow to package plugin on CI/CD

[Guts]

To be merged after #21

In this PR, a GitHub workflow to:

• package the plugin on every PR where plugin's files have been modified
• release it as GitHub Release
• publish it automatically to official QGIS repository (see below)

@kannes to make the workflow work, you have to set your plugins.qgis.org credentials as GitHub Actions Secrets (OSGEO_PASSWORD and OSGEO_USER). Screenshot from QTribu:

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• Related to Profile Manager x QGIS Deployment Toolbelt: an impacting contribution proposal #10
• ❤️ Funded by Oslandia and ANFSI.

[kannes]

Oh nice! Tbh we do not have a technical account for this yet but all our plugins are maintained by different people and their accounts... It's something we were just discussing internally the other day. Is there a standard process that you can recommend? Does OSGeo allow technical accounts? I'd like to not use my personal account for this.

[Guts]

We use the oslandia account at Oslandia and the geotribu account at Geotribu but TBH it's not so important I think, personal account is OK. Iwas using it for QTribu until recently. You just need to use credentials of an user who is authorized to publish a new version of the plugin (owner or maintainer level on https://plugins.qgis.org).

For a few months, API token are available but it's still not supported in QGIS Plugin CI (opengisch/qgis-plugin-ci#285).

[jmkerloch]

Again every thing looks OK to me 🚀

[kannes]

I have set up the secrets with my personal account for now and switch to the technical account once we have it.