feat: support shared bucket for backups

[shreddedbacon]

Checklist

• Affected Issues have been mentioned in the Closing issues section
• Documentation has been written/updated
• PR title is ready for inclusion in changelog

As described in #3444 there is a limit on how many buckets there can be in S3.

This changes the behaviour of new projects to use a bucket derived from the deploytarget name, or from a defined sharedBaasBucketName field on the deploytarget.

There is currently a LAGOON_BAAS_BUCKET_NAME override variable that can also be defined in a project, so this still overrides the shared bucket even if the project is new. To revert to the shared bucket in this case is to simply delete the LAGOON_BAAS_BUCKET_NAME variable.

The change will now create the k8up path like so.

${sharedBaasBucketName}/baas-${projectName}

To convert an existing project to use the shared bucket, you will need to check for the existence of the override variable and remove it, and then update the project in the Lagoon API to set the projects sharedBaasBucket=true (platform-owner role required). This has the negative effect that it basically makes all the existing backups unusable. So transferring the data somehow will need to be done if you wish to retain those backups. A deployment will also need to be performed after setting the sharedBaasBucket value.

This requires uselagoon/build-deploy-tool#219 to work

Closing issues

closes #3444

[rocketeerbkw]

LGTM