Rename Samba's DCO to Samba Developer's Declaration after CC-BY-SA 4.0 compliance for the text

As you know, it's rare that Conservancy offers specific patches upstream to our projects. This is a rare exception since it relates to licensing policy.

As many of you may know, Jeremy Allison originally requested that the Samba's Contributor Representation be named DCO as a tribute to Linux and its DCO.

But, for a variety of reasons, I (with this patch recommend to change the name. Also included is some cleanup work regarding the copyright and license on the DCO text itself.

Note that since the CC-BY-SA compliance in !1610 (closed) absolutely needs to happen before this, I've made this a change on top of that. !1610 (closed) will need to be merged first and I added it to the checklist. I assume/hope Gitlab can handle the fact that the CC-BY-SA change also appears here. I tested it with a normal "git merge" on the Git CLI and it worked fine.

Note that this

Checklist (I believe unchecked items are N/A for this case)

• MR !1610 (closed) has already been merged first.
• Commits have Signed-off-by: with name/author being identical to the commit author
• Documentation updated
• CI timeout is 3h or higher (see Settings/CICD/General pipelines/ Timeout)

Reviewer's checklist:

• This feature/change has adequate documentation added
• No obvious mistakes in the code