feat(index/remove): add output messages for index remove command

[alacuku]

Furthermore debug messages are printed when --verbose flag is set.

What type of PR is this?

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/kind bug

/kind cleanup

/kind design

/kind documentation

/kind failing-test

/kind feature

/kind flaky-test

Any specific area of the project related to this PR?

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/area library

/area cli

/area tests

/area examples

What this PR does / why we need it:
Add output messages for falcoctl index remove command. The following snippet shows the outputs when running the command with `--verbose flag set to true:

❯ falcoctl index remove falcosecurity falcosecurity1 -v
 INFO  Creating in-memory cache using indexes file "/home/aldo/.config/falcoctl/indexes.yaml" and indexes directory "/home/aldo/.config/falcoctl/indexes"
 INFO  Removing index "falcosecurity"
 INFO  Removing index "falcosecurity1"
 INFO  Writing cache to disk
 INFO  Removing indexes entries from configuration file "/etc/falcoctl/falcoctl.yaml"
 INFO  Indexes successfully removed

Which issue(s) this PR fixes:
Give visibility to end users of what is happening under the hood when removing existing indexes.

Fixes #

Special notes for your reviewer:

[cpanato]

/lgtm

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alacuku, cpanato

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[poiana]

LGTM label has been added.

Git tree hash: 178329cc76be60b51d946f849bbed17ceae38555