feat: add script for building rocks via lpci

[cjdcordeiro]

In this PR there is a new standalone Python script that takes a rockcraft.yaml file from the current directory and offloads the corresponding builds to Launchpad, via lpci.

How does it work?

1. the user provides a valid LP credential (or creates one during the first run of the script, interactively)
2. a local Git repo is created in a temporary folder, and all the contents from the user's current directory are copied there
3. a .launchpad.yaml configuration file is created in this temporary git repo. The yaml file is populated according to the rockcraft.yaml's build-base and platforms
4. a brand new repo (with a time-based identifier) is created in Launchpad
5. the local temporary git repo, with the .launchpad.yaml file, is pushed to the newly created LP repo
6. the above step automatically triggers the CI builds in Launchpad
7. the script keeps fetching those builds' statuses until they are all complete
8. finally, for the successful builds, the rock artefacts (aka OCI archives) are downloaded into the current directory

Try it

To try it, you can simply

pip install -r requirements.txt
./requirements.sh
rockcraft init   # to get a demo rockfile to play with
./rockcraft_lpci_build.py --lp-credentials-file <path-to-where-you-want-to-save-your-creds> --allow-build-failures 

[linostar]

Add a README with the following steps:

How to use:

1. Clone the repo and go to rockcraft_lpci repo. Optionally, create a virtualenv dir there and activate the virtualenv
2. Run: pip install -r requirements.txt
3. Run: ./requirements.sh
4. Create/move your rockcraft.yaml in the current dir
5. Run: python3 rockcraft_lcpi_build.py --allow-build-failures --lp-credentials-file <path-to-where-you-want-to-save-your-creds> 

[linostar]

Is the --lp-credentials-b64 argument necessary? It apparently requires the oauth token/secret encoded in base64, but it doesn't tell the user that explicitly, plus the user has to create the oauth token manually.

[linostar]

I am not sure if this is a desired effect, but I'll mentioned it here.
Whenever a build fails, launchpad sends an email notification containing a link to the build log. However, if you are not fast enough the build logs link will give 404 because the temporary repo will be deleted once all builds are done even if they fail.

[cjdcordeiro]

I am not sure if this is a desired effect, but I'll mentioned it here. Whenever a build fails, launchpad sends an email notification containing a link to the build log. However, if you are not fast enough the build logs link will give 404 because the temporary repo will be deleted once all builds are done even if they fail.

Y that's the case. I could add an option to "--keep-repo-alive". But since the script downloads the logs, I don't think there's a need for that.

[linostar]

Looks good to go.

[cjdcordeiro]

@linostar this is ready for review. the unit tests are still very minimal, but we might just go ahead with them like this just to get something started for now

[linostar]

A wholesome effort. Great work.