fix: no logs when there is no source

[lemeurherve]

Fixes #617
Supersedes #640

Don't output anything about source when there isn't any sources section.

Test

To test this pull request, you can run the following commands:

./dist/updatecli diff --values examples/values.yaml --config examples/updatecli.d/updatecli-no-sources.yaml

With https://github.com/updatecli/updatecli/blob/main/examples/updatecli.d/updatecli.yaml without its sources block:

Before:

#############################
# UPDATECLI-NO-SOURCES.YAML #
#############################


SOURCES
=======


CONDITIONS:
===========
WARNING: The directive 'scm' for the condition["dockerFile"] is now deprecated. Please use the new top level scms syntax
WARNING: The directive 'scm' for the target["dockerFile"] is now deprecated. Please use the new top level scms syntax

[...]

After:

#############################
# UPDATECLI-NO-SOURCES.YAML #
#############################


CONDITIONS:
===========
WARNING: The directive 'scm' for the condition["dockerFile"] is now deprecated. Please use the new top level scms syntax
WARNING: The directive 'scm' for the target["dockerFile"] is now deprecated. Please use the new top level scms syntax

[...]

Additional Information

Tradeoff

Potential improvement

[olblak]

can you elaborate why you closed the Pullrequest #640 in favor of this one? I think I preferred the other approach even though I couldn't tested it yet

[lemeurherve]

Because In my previous PR these ifs (L13 of each stage file like https://github.com/lemeurherve/updatecli/blob/cb37b0bf1efcf8bcee09f9e26f55f3bcf7245a00/pkg/core/pipeline/conditions.go#L13) were useless since the calls to Run<Stage> are already inside if len(p.<stages>) > 0 blocks for conditions, targets and pullrequests stages.

Thus, I prefered doing the same for sources instead of adding conditional instructions never reached for conditions & targets.

[olblak]

Because In my previous PR these ifs (L13 of each stage file like https://github.com/lemeurherve/updatecli/blob/cb37b0bf1efcf8bcee09f9e26f55f3bcf7245a00/pkg/core/pipeline/conditions.go#L13) were useless since the calls to Run<Stage> are already inside if len(p.<stages>) > 0 blocks for conditions, targets and pullrequests stages.

Thus, I prefered doing the same for sources instead of adding conditional instructions never reached for conditions & targets.

It makes a lot of sense, thank you for looking into this