[installer] Allow the use of a static password for the message bus

[andrew-farries]

Description

One of the Webapp team's epics for Q2 is to use the Gitpod installer to deploy to Gitpod SaaS. In order to do that we will need to add additional configuration to the installer to make the output suitable for a SaaS deployment as opposed to a self-hosted deployment.

This PR adds an experimental.common.staticMessagebusPassword field to set a message bus password, rather than having the installer render a fresh password on every invocation. cf this comment from @mrsimonemms.

Related Issue(s)

Part of #9097

How to test

Create an installer config file containing this experimental section:

experimental:
  common:
    staticMessagebusPassword: "some-password"

Get a versions.yaml for use with the installer:

docker run -it --rm "eu.gcr.io/gitpod-core-dev/build/versions:${version}" cat versions.yaml > versions.yaml

Then invoke the installer as:

go run . render --debug-version-file versions.yaml --config /path/to/config --use-experimental-config

The message bus password will be the value set in the config. If the experimental config section is omitted, or the staticMessagebusPassword is set to an empty string, a password will be generated.

Release Notes

Add `staticMessagebusPassword` config flag to use a fixed message bus password in the installer

Documentation

None.

[geropl]

Nice, thank you for the tests! 🧡