[VOL-5545] Update voltha docs

- release notes for VOLTHA versions 2.6 to 2.15 with new Jira links and adjust release schedule details
- update old links
- remove ONF references and links
- update e-mail links
- update copright notices

Change-Id: Id6be18986a8f52f2dfcc07e2b0d2efcb0ae1c0e4
Signed-off-by: serkant.uluderya <serkant.uluderya@netsia.com>
diff --git a/_static/css/rtd_theme_mods.css b/_static/css/rtd_theme_mods.css
index 1e3f8d9..086d0ac 100644
--- a/_static/css/rtd_theme_mods.css
+++ b/_static/css/rtd_theme_mods.css
@@ -1,5 +1,5 @@
 /*
- * Copyright 2019-2023 Open Networking Foundation (ONF) and the ONF Contributors
+ * Copyright 2019-2023 Linux Foundation Broadband Contributors
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.