docs: add howto guides for switching from the charm plugin

[lengau]

This adds howto guides to switch from the charm plugin to the python and poetry plugins.

[mattculler]

Very clear!

[jnsgruk]

Gave this a go here: jnsgruk/zinc-k8s-operator#288

Might be worth including a section about using override-pull as a place where people can generate requirements'txt if they need to.

I guess they could also use override-build and just place their generation code before craftctl default.

Edit: lots of failed integration tests when I changed to this; will investigate.

[jnsgruk]

Heh. The python plugin doesn't seem to have included any dispatch file...

ubuntu@ubuntu-noble-2e39:~/zinc_charm_unzipped$ ls -la
total 39480
drwxrwxr-x 5 ubuntu ubuntu     4096 Oct 18 10:30 .
drwxr-xr-x 9 ubuntu ubuntu     4096 Oct 18 10:30 ..
drwxrwxr-x 2 ubuntu ubuntu     4096 Oct 18 10:30 bin
drwxrwxr-x 3 ubuntu ubuntu     4096 Oct 18 10:30 lib
drwxrwxr-x 3 ubuntu ubuntu     4096 Oct 18 10:30 lib64
-rw-r--r-- 1 ubuntu ubuntu      255 Oct 18 10:21 manifest.yaml
-rw-r--r-- 1 ubuntu ubuntu     1402 Oct 18 10:21 metadata.yaml
-rw-r--r-- 1 ubuntu ubuntu      169 Oct 18 10:21 pyvenv.cfg

Edit: switched to the latest/edge channel and things seem better:

ubuntu@ubuntu-noble-2e39:~/data/code/charms/zinc-k8s-operator$ unzip -l ./zinc-k8s_amd64.charm | grep -v python3
Archive:  ./zinc-k8s_amd64.charm
  Length      Date    Time    Name
---------  ---------- -----   ----
      272  2024-10-18 10:38   manifest.yaml
     1402  2024-10-18 10:38   metadata.yaml
      673  2024-10-18 10:38   dispatch
      188  2024-10-18 10:34   venv/pyvenv.cfg
     2680  2024-10-03 08:44   src/zinc.py
     3922  2024-10-03 08:44   src/charm.py
        0  2022-05-31 14:57   src/prometheus_alert_rules/.gitkeep
      294  2022-07-30 20:33   src/prometheus_alert_rules/zinc_missing.rule
        0  2022-05-31 14:57   src/loki_alert_rules/.gitkeep
    20957  2023-08-23 13:19   src/grafana_dashboards/zinc.json.tmpl
    99854  2024-08-19 14:12   lib/charms/loki_k8s/v0/loki_push_api.py
    30560  2024-08-28 16:53   lib/charms/traefik_k8s/v2/ingress.py
    96662  2024-08-19 14:12   lib/charms/prometheus_k8s/v0/prometheus_scrape.py
    34280  2024-10-02 08:52   lib/charms/parca/v0/parca_scrape.py
    80536  2024-08-19 14:12   lib/charms/grafana_k8s/v0/grafana_dashboard.py
     9975  2024-10-02 08:52   lib/charms/observability_libs/v0/juju_topology.py
---------                     -------
 41499875                     2412 files

Alas, no dice on deploying, though...

ubuntu@ubuntu-noble-2e39:~/zinc_charm/venv$ juju debug-log
unit-zinc-k8s-0: 10:39:59 WARNING unit.zinc-k8s/0.install ln: failed to create symbolic link '/var/lib/juju/agents/unit-zinc-k8s-0/charm/venv/bin/python': No such file or directory
unit-zinc-k8s-0: 10:39:59 WARNING unit.zinc-k8s/0.install /var/lib/juju/agents/unit-zinc-k8s-0/charm/dispatch: 16: exec: /var/lib/juju/agents/unit-zinc-k8s-0/charm/venv/bin/python: not found
unit-zinc-k8s-0: 10:39:59 ERROR juju.worker.uniter.operation hook "install" (via hook dispatching script: dispatch) failed: exit status 127