EUDC: Add eudc-ignore-options-file customization

EUDC: Add eudc-ignore-options-file customization

* etc/NEWS (EUDC): Document eudc-ignore-options-file.
* doc/misc/eudc.texi (The Server Hotlist): Likewise
* lisp/net/eudc-vars.el (eudc-ignore-options-file): New variable.
(eudc-options-file): Mention new variable.
* lisp/net/eudc.el: Warn on load if eudc-ignore-options-file is
set but the options file exists.
(eudc-set-server): Support
eudc-ignore-options-file.
(eudc-bookmark-server): Likewise.
(eudc-save-options): Likewise.  (Bug#56154)