Use testify instead of native testing library

[mmorel-35]

What would you like to be added?

Testify is more concise and have a lot functions that holds default messages that needs to be explicitly wrote with native testing package.

The completion track is as follows:

• fix: use testify instead of t.Fatal or t.Error in server package (part 1) #18971
• fix: use testify instead of t.Fatal or t.Error in pkg package (part 1) #18970
• fix: use testify instead of t.Fatal or t.Error in etcdctl packages #18969
• fix: use testify instead of t.Fatal or t.Error in contrib package #18968
• fix: use testify instead of t.Fatal or t.Error in client package (part 1) #18967
• fix: use testify instead of t.Fatal or t.Error in api package #18966
• fix: use testify instead of t.Fatal in tests/common package (part 2) #18860
• fix: use require instead of t.Fatal(err) in tests/common package #18823
• fix: use require instead of t.Fatal(err) in tests/e2e package #18821
• fix: use require instead of t.Fatal(err) in tests/integration package #18820
• fix: use require instead of t.Fatal(err) in tests/robustness package #18782
• fix: use require.NoError instead of t.Fatal(err) in tests package (part 1) #18753
• fix: use require.NoError instead of t.Fatal(err) in contrib and tools packages #18752
• fix: use require.NoError instead of t.Fatal(err) in client package #18705

[ahrtr]

All done. Thanks @mmorel-35