feat: extend integration tests for experiments

[NohaIhab]

Summary of changes:

• make katib experiment test parametrizable
• refactor test directory into utils and tests
• test deletion of experiment
• add examples for all images mentioned in Integration tests for Katib experiments #103

CI changes:

• remove unused microk8s metallb addon
• added step in integrate.yaml to maximise GH runner space

Note: controller integration tests failing recorded in #119, the controller charm was not touched in this PR.

[i-chvets]

Just a comment on re-organization of test data. A strong suggestion, since we starting to introduce a better organization for our tests in other charms.
Test data is organized in this format (except in your case you do not have data/, since there is no need):

tests/
├── assets
│   ├── crs
│   │   ├── grid-example.yaml
│   │   └── file-metrics-collector.yaml
│   └── data # no need for this folder, just an illustration
│       └── <some-future-json-data>