Jkube: EnvUtilTest.java: Replace hamcrest with AssertJ

[manusa]

Description

We are replacing the usage of Hamcrest assertions with AssertJ all over the project.

In EnvUtilTest.java, replace any usage of Hamcrest with the AssertJ (org.assertj.core.api.Assertions.assertThat).

e.g.
https://github.com/eclipse/jkube/blob/813074705147f9423dd807385c0d40e4670ddf9a/jkube-kit/common/src/test/java/org/eclipse/jkube/kit/common/util/EnvUtilTest.java#L401

should be changed to:

        assertThat(timestamp).isEqualTo(new Date(1445385600000L));

Bonus

Replace the rest of assertions (org.junit.Assert.*) with AssertJ too.

[himanshu007-creator]

Hi, i would like to work on this issue

[ramananrpn]

Hey, shall I pick it up if you didn't started ? @himanshu007-creator

[himanshu007-creator]

Hey, shall I pick it up if you didn't started ? @himanshu007-creator

Sure!, @manusa please assign @ramananrpn this issue. 🟩

[ramananrpn]

@manusa @rohanKanojia Could you guys please review and merge this PR #789 ?