Add user blocking (#29028)

Fixes #17453

This PR adds the abbility to block a user from a personal account or
organization to restrict how the blocked user can interact with the
blocker. The docs explain what's the consequence of blocking a user.

Screenshots:


![grafik](4ed884f3-e06a-4862-afd3-3b8aa2488dc6)


![grafik](ae6d4981-f252-4f50-a429-04f0f9f1cdf1)


![grafik](ca153599-5b0f-4b4a-90fe-18bdfd6f0b6b)

---------

Co-authored-by: Lauris BH <lauris@nix.lv>

tests/integration/api_issue_reaction_test.go

@@ -58,6 +58,13 @@ func TestAPIIssuesReactions(t *testing.T) {
 	// Add existing reaction
 	MakeRequest(t, req, http.StatusForbidden)
 
+	// Blocked user can't react to comment
+	user34 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 34})
+	req = NewRequestWithJSON(t, "POST", urlStr, &api.EditReactionOption{
+		Reaction: "rocket",
+	}).AddTokenAuth(getUserToken(t, user34.Name, auth_model.AccessTokenScopeWriteIssue))
+	MakeRequest(t, req, http.StatusForbidden)
+
 	// Get end result of reaction list of issue #1
 	req = NewRequest(t, "GET", urlStr).
 		AddTokenAuth(token)