docs: add headerBackTestID option in Header component

Author: tranquanghuy0801

versioned_docs/version-6.x/elements.md

@@ -116,6 +116,10 @@ Color for material ripple (Android >= 5.0 only)
 
 Press opacity for the buttons in header (Android < 5.0, and iOS)
 
+#### `headerBackTestID`
+
+TestID used on the back button. Useful for e2e testing with Detox.
+
 #### `headerTransparent`
 
 Defaults to `false`. If `true`, the header will not have a background unless you explicitly provide it with `headerBackground`. The header will also float over the screen so that it overlaps the content underneath.

versioned_docs/version-7.x/elements.md

@@ -116,6 +116,10 @@ Color for material ripple (Android >= 5.0 only)
 
 Press opacity for the buttons in header (Android < 5.0, and iOS)
 
+#### `headerBackTestID`
+
+TestID used on the back button. Useful for e2e testing with Detox.
+
 #### `headerTransparent`
 
 Defaults to `false`. If `true`, the header will not have a background unless you explicitly provide it with `headerBackground`. The header will also float over the screen so that it overlaps the content underneath.