[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/overview/contributing/copyright/markdown.rst b/overview/contributing/copyright/markdown.rst
index e57068e..8082acd 100644
--- a/overview/contributing/copyright/markdown.rst
+++ b/overview/contributing/copyright/markdown.rst
@@ -6,7 +6,8 @@
 
    <!--
    # -----------------------------------------------------------------------
-   # Copyright 2017-2024 Open Networking Foundation Contributors
+   # Copyright 2017-2026 Linux Foundation Broadband Contributors
+   # Copyright 2017-2024 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.
@@ -20,7 +21,7 @@
    # See the License for the specific language governing permissions and
    # limitations under the License.
    # -----------------------------------------------------------------------
-   # SPDX-FileCopyrightText: 2017-2024 Open Networking Foundation Contributors
+   # SPDX-FileCopyrightText: 2017-2026 Linux Foundation Broadband Contributors
    # SPDX-License-Identifier: Apache-2.0
    # -----------------------------------------------------------------------
    # Intent: