Add script to generate manifest with default config

[carles-grafana]

The script:

• generates the manifest with default config YAML which is included in the docs as a reference.
• runs in CI to check if the manifest needs to be updated as a result of new changes in the default config.

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[mapno]

Should this be a make target?

[carles-grafana]

personally I'm not a fan of putting this kind of commands in the makefile as it tends to grow a lot, but I'm fine with it if it's the team convention

[javiermolinar]

I rather use make as well. That's its main purpose

[carles-grafana]

Added to Makefile.

[carles-grafana]

Something to keep in mind is that every time we run make, some commands are run which add an overhead:

# Version number
VERSION=$(shell ./tools/version-tag.sh | cut -d, -f 1)

GIT_REVISION := $(shell git rev-parse --short HEAD)
GIT_BRANCH := $(shell git rev-parse --abbrev-ref HEAD)

For now this is negligible, but as the Makefile grows we are more likely to introduce significant overhead. I've seen this in my previous job where we had a giant Makefile, that's why I'm averse to it and I would rather not use make as a generic task runner.

[carles-grafana]

By managing to reuse the build cache, now the new command only takes 2 seconds, I just had the use the exact same build flags GO111MODULE=on CGO_ENABLED=0 in order to reuse the cache

[mapno]

LGTM!