feat(opc): [SPE-29] Add configuration variable is_guest_checkout_enab…

[kevin-carangeot]

…led for template

Questions	Answers
Branch?	develop / 9.1.x / 9.0.x
Description?	Please be specific when describing the PR. Every detail helps: versions, browser/server configuration, specific module/theme, etc. Feel free to add more information below this table.
Type?	bug fix / improvement / new feature / refacto
Category?	FO / BO / CO / IN / WS / TE / LO / ME / PM / see explanations at https://devdocs.prestashop-project.org/9/contribute/contribution-guidelines/pull-requests/#type--category
BC breaks?	yes / no
Deprecations?	yes / no
How to test?	Indicate how to verify that this change works as expected.
UI Tests	Please run UI tests and paste here the link to the run. As we support MySQL and MariaDB in our tests, you have to launch 2 campaigns (by choosing both). Visit the UI Tests repo and follow instructions.
Fixed issue or discussion?	Fixes #{issue number here}, Fixes #{another issue number here}, Fixes https://github.com/PrestaShop/PrestaShop/discussions/ {discussion number here}
Related PRs	If theme, autoupgrade or other module change is needed to make this change work, provide a link to related PRs here.
Sponsor company	Your company or customer's name goes here (if applicable).