Add a flag -o/--output to kubermatic-installer to allow json output

[embik]

What does this PR do / Why do we need it:
Not sure if we want to merge this, but I thought it would be neat to have the option for json log formatting in kubermatic-installer. The default of course stays with the nice formatter that logrus uses for human readability (filled under "console" in this new flag), but an --output (or shorthand -o) flag will allow to get json output if that is wanted (I can see this being useful with the upcoming mirror-images subcommand, for example).

This is what it would look like, as an example for an early failure on deploying:

$ ./_build/kubermatic-installer deploy
INFO[0000] 🚀 Initializing installer…                     edition="Enterprise Edition" version=2a9ece9131272f12e01b6331769fdd301239230d
ERRO[0000] ❌ Operation failed: no kubeconfig (--kubeconfig or $KUBECONFIG) given.

$  ./_build/kubermatic-installer deploy -o json
{"edition":1,"level":"info","msg":"🚀 Initializing installer…","time":"2022-06-21T17:00:30+02:00","version":"2a9ece9131272f12e01b6331769fdd301239230d"}
{"level":"error","msg":"❌ Operation failed: no kubeconfig (--kubeconfig or $KUBECONFIG) given.","time":"2022-06-21T17:00:30+02:00"}

WDYT?

Does this PR close any issues?:
Fixes #

Special notes for your reviewer:

Documentation:

Does this PR introduce a user-facing change?:

`kubermatic-installer` output can be formatted as json via a new `--output` flag

Signed-off-by: Marvin Beckers marvin@kubermatic.com

[embik]

/retest

[xrstf]

Not sure what's so neat about this in this case, but I only have minor things to mention:

• In all other apps, we use -log-format, should we use the same here instead of -o? I don't mind -o, just wondering.
• The log messages do have indentations, so we would end up with something like "msg:" foo". Can you live with that? (I tried sooo hard to somehow automate the indentation somehow, as if it was structured logging, but manually indenting all lines was much easier, hence the many empty spaces).

[embik]

In all other apps, we use -log-format, should we use the same here instead of -o? I don't mind -o, just wondering.

I was thinking about that, but since we're already doing different logging in the installer, I thought offering something that looks more like other Kubernetes client applications was better. I don't have strong opinions about that though, I can change it if you prefer it to be consistent.

The log messages do have indentations, so we would end up with something like "msg:" foo". Can you live with that? (I tried sooo hard to somehow automate the indentation somehow, as if it was structured logging, but manually indenting all lines was much easier, hence the many empty spaces).

I don't think that's an issue 🤷🏻

[xrstf]

/approve
/lgtm

I wish we had telemetry to tell us how many users discovered and then used the JSON output in the future :D

[kubermatic-bot]

LGTM label has been added.

Git tree hash: f3d82d414ce7700c7a978a72f8f108cb5796dd9b

[kubermatic-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: embik, xrstf

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[embik]

/retest

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[kubermatic-triage-bot]

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