[FIX] web: Make datetime options help text clearer

Steps:

Install web_studio
Change language to French
Open any form view and enable Studio
Add a datetime field and click on it
In french we have the following message:
"Première date acceptée": Date formatée ISO ou "aujourd'hui" He says that we can use the string "aujourd'hui"
when we only expect "today" in English.

This commit changes the help text to display "today" in every language

opw-3829954

closes odoo/odoo#160904

Forward-port-of: #160144
Forward-port-of: #159654
Signed-off-by: Achraf Ben Azzouz (abz) <abz@odoo.com>

addons/web/i18n/web.pot

@@ -3492,7 +3492,7 @@ msgstr ""
 #: code:addons/web/static/src/views/fields/datetime/datetime_field.js:0
 #: code:addons/web/static/src/views/fields/datetime/datetime_field.js:0
 #, python-format
-msgid "ISO-formatted date (e.g. \"2018-12-31\") or \"today\"."
+msgid "ISO-formatted date (e.g. \"2018-12-31\") or \"%s\"."
 msgstr ""
 
 #. module: web

addons/web/static/src/views/fields/datetime/datetime_field.js

@@ -277,13 +277,13 @@ export const dateField = {
             label: _t("Earliest accepted date"),
             name: "min_date",
             type: "string",
-            help: _t(`ISO-formatted date (e.g. "2018-12-31") or "today".`),
+            help: _t(`ISO-formatted date (e.g. "2018-12-31") or "%s".`, "today"),
         },
         {
             label: _t("Latest accepted date"),
             name: "max_date",
             type: "string",
-            help: _t(`ISO-formatted date (e.g. "2018-12-31") or "today".`),
+            help: _t(`ISO-formatted date (e.g. "2018-12-31") or "%s".`, "today"),
         },
         {
             label: _t("Warning for future dates"),