Pass the --filter flag to the Botkube executor plugins

[mszostok]

Overview

The --filter flag is globally reserved by Botkube. That means that all other plugins cannot use it.

However, Helm has its own support for the --filter flag in helm list --filter 'ara[a-z]+'. It's more advanced as:

• table headers are not removed from the output,
• regex is fully supported,
• and also only the release names are compared (not the whole line).

As a workaround, in the helm list command we use -f instead of --filter. However, this breaks the helm list contract and user needs to adjust the command before running it via Botkube which provides a bad UX.

Acceptance Criteria

• The --filter flag, if specified, is passed to the Botkube executor plugins

Options

• switch to pipes instead of flag. For example, kc get po -A | grep 'k.*'. We can implement the grep plugin and do command split on | and support command chaining.
• use different syntax for filter flag, e.g. @filter instead of --filter
• Extend the ExecutorOutput struct and add isResultFiltered, if yes, then we don't run our own filtering.

Notes

We should think about general approach to the Botkube related flags, to make sure that we will not have similar problem in the future.