[kibana-plugin CLI] add optimize task and skip-optimize option on install task

[gwintzer]

Hi,

Here's a PR according to the issue #6057.

• Add a new optimize task to the kibana-plugin CLI
• Add an option --skip-optimize for the existing install task

Example :

# install all your plugins faster
./bin/kibana-plugin install --skip-optimize plugin1
./bin/kibana-plugin install --skip-optimize plugin2

# finally run the optimize task once
./bin/kibana-plugin optimize

[elasticmachine]

Can one of the admins verify this patch?

[epixa]

@gwintzer Thanks for the PR, but we're no longer adding any features to 5.6. Can you retarget this for master instead? This ensures that the feature is available in all future versions, and we'll backport the change down to the next feature release.

[FireBurn]

Is there a version anywhere that applies to version 6?

[gwintzer]

I will try to retarget the PR on master soon to allow a backport on v5/v6

[epixa]

@gwintzer Thanks for opening up a new PR against master. I'm going to close this one in favor of that one.

PR against master: #14991