merge release notes into a single file

Test-Management/release-note.md

Test-Management/release-notes/5_4_2.md

Test-Management/release-notes/5_5_0.md

Test-Management/release-notes/5_5_7.md

Test-Management/release-notes/5_6_0.md

Test-Management/release-notes/5_7_0.md

Test-Management/release-notes/5_7_2.md

Test-Management/release-notes/5_7_3.md

Test-Management/release-notes/5_8_0.md

Test-Management/release-notes/5_9_0.md

Test-Management/release-notes/5_9_1.md

Test-Management/release-notes/5_9_2.md

Test-Management/release-notes/5_9_3.md

Test-Management/release-notes/5_9_4.md

Test-Management/release-notes/5_9_5.md

Test-Management/release-notes/5_9_6.md