docs: replace 'Edit on GitLab' with 'View page source'

docs: replace 'Edit on GitLab' with 'View page source'

QEMU takes contributions via the mailing list, so while you can edit a
file on gitlab and then switch to the terminal to send a patch, the
wording 'Edit on GitLab' strongly suggests we take merge requests.

Switching back to "View page source" is a more agnostic term that does
not imply a particular contribution approach, that we had used in QEMU
before:

  commit 73e6aec6522e1edd63f631c52577b49a39bc234f
  Author: Marc-André Lureau <marcandre.lureau@redhat.com>
  Date:   Tue Mar 23 15:53:28 2021 +0400

    sphinx: adopt kernel readthedoc theme

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-ID: <20241209163506.2089961-1-berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>