Revert "[Side search clean-up] Remove features::kSideSearch"

This reverts commit bba0f62673780eb5e63806425e39bcae46883d6c.

Reason for revert: Need finch control of side search so we can run holdback experiments.

Original change's description:
> [Side search clean-up] Remove features::kSideSearch
>
> This CL removes Flag kSideSearch that has been enabled by default.
>
> Bug: 1401094
> Change-Id: I81a6c48cde5fd1e6b16f53379dcbc229a19a63da
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4182976
> Commit-Queue: pengchao Cai <[email protected]>
> Reviewed-by: Yuheng Huang <[email protected]>
> Cr-Commit-Position: refs/heads/main@{#1095360}

Bug: 1401094, 277819250
Change-Id: I947a941c8934e22ef8ff342a56dc5122ec7062a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4415647
Commit-Queue: Michael Crouse <[email protected]>
Reviewed-by: Thomas Lukaszewicz <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1129023}
diff --git a/chrome/browser/flag_descriptions.cc b/chrome/browser/flag_descriptions.cc
index 2efca72..f284a2c 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -6679,6 +6679,11 @@
     "Enable the new password managment bubble triggered by clicking the key "
     "icon in the omnibox.";
 
+const char kSideSearchName[] = "Side search";
+const char kSideSearchDescription[] =
+    "Enables an easily accessible way to access your most recent Google search "
+    "results page embedded in a browser side panel";
+
 const char kSearchWebInSidePanelName[] = "Search web in side panel";
 const char kSearchWebInSidePanelDescription[] =
     "Displays right-click search results of a highlighted text in side panel";