Library upgrade, base JDK8 and JDK16 compatiblity

Base Java 8 upgrade

Bump jdk to 8; Bump assertj to 3.19.0; remove assertj-7 module #48

Fixed the dependency management section

Stop managing versions other than jsonpath #42

Library upgrades:

Bumped jackson to 2.12.2 #54
Bumped groovy and spock to 3.0.7 & 2.0-M5 #53
Bump cglib to 3.3.0 #52
Bump objenesis to 3.2 #51
Bump logback classic to 1.2.3 #50
Bump gmaven plus plugin to 1.21.1 #49
Bumped gson to 2.8.6 #47
Bump org.json:json to 202010307 #46
Bumped tapestry-json to 5.7.1 #45
Bumped jettison to 1.4.1 #44
Bumped shade plugin to 3.2.4 #43
Upgrade JsonPath library to 2.5 #40