add(configuration): ability to store configuration in [tool:qgis-plugin-ci] section in plugin's metadata.txt

[Guts]

Description

We already reading/writing the plugin's metadata.txt so why not loading full config from there? Well, talking with colleagues, from a plugin dev perspective, it looks like a good idea to store everything in the same config file.

@Xpirix @timlinux is there a risk to see this extra section spotted by checks running at publish time?

plugin_path is still mandatory but maybe we could add a small lookup logic tyo find it (as parent folder of the metadata.txt) in a next PR?

I used claude.ai to write unit tests.

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[3nids]

Tihs makes sense to me.
Some thoughts though:

• adding a 4th config option for me should wait for v3. There we decide for a single source of truth to reduce code quantity and chances of different behaviors? -- maybe 2, but not 4 ;)
• I guess this will mean adding a new param to the CLI to give it the location of the metadata file (this will be one parameter less for the plugin path). Other options are non valid for me (moving/copying or configuring) since that would mean a required building step to test the plugin while you develop.

I'm just seeing the need for a cleanup before putting more, but I'm ok to make it land in v2 if you want to, no strong opinion.

[Xpirix]

is there a risk to see this extra section spotted by checks running at publish time?

I don't think so. I guess the checks are mainly checking on missing mandatory fields rather than extra ones and wouldn't probably take them into consideration (not saved in the DB, will stay in the metadata) if not declared in the validators.