feat: add build tag to enable libjq-go explicitly

[diafour]

Overview

• use jq binary by default to simplify local setup and testing
• build tag 'use_libjq' should be used to build shell-operator with libjq-go
• add debug message with jqFilter implementation details

What this PR does / why we need it

libjq-go is somewhat hard to install when you want just run tests on new PR.

Results

# CGO_ENABLED=1 is by default, jq binary is used now.
$ go build ./cmd/shell-operator                                                                  
$ LOG_LEVEL=Debug ./shell-operator
time="2022-11-28T10:22:47+03:00" level=debug msg="Use jq binary for jqFilter"

# jq binary will be used if CGO_ENABLED=0, as before.
$ CGO_ENABLED=0 go build ./cmd/shell-operator
$ LOG_LEVEL=Debug ./shell-operator            
time="2022-11-28T10:25:35+03:00" level=debug msg="Use jq binary for jqFilter"

# To compile with libjq-go add build tag 'use_libjq'
$ go build -tags use_libjq ./cmd/shell-operator
$ LOG_LEVEL=Debug ./shell-operator             
time="2022-11-28T10:23:13+03:00" level=debug msg="Use libjq-go for jqFilter"

# Set JQ_EXEC=yes at runtime to enable executing jq binary (e.g. for debug purposes).
$ JQ_EXEC=yes LOG_LEVEL=Debug ./shell-operator 
time="2022-11-28T10:23:23+03:00" level=debug msg="JQ_EXEC is set, use jq binary for jqFilter"