selectrum: improve ivy parity

- add `:pg` bindings
- add `selectrum-minibuffer-map` to `+default-minibuffer-maps`
- add `consult-notmuch`
- add selectrum option for `mu4e-completing-read-function`
- document more parity failings

modules/email/notmuch/config.el

@@ -103,3 +103,9 @@ OR a shell command string such as
   :when (featurep! :completion helm)
   :commands helm-notmuch
   :after notmuch)
+
+
+(use-package! consult-notmuch
+  :when (featurep! :completion selectrum)
+  :commands consult-notmuch
+  :after notmuch)