Changed POST API saml_group_links to accept acccess_level as integer

What does this MR do and why?

This MR is in continuation with ISSUE#290367

Current behaviour of saml_group_links API implementation where we are accepting access_level as type string is not consistent with other group API implementations where access_level is accepted as type integer.

As per discussion on the main issue - #290367 (comment 1065245671) , This MR corrects the behaviour by making API calls to accept access_level as integer.

Behaviour is now consistent with rest of the API calls for group as observed here - https://docs.gitlab.com/ee/api/groups.html#add-ldap-group-link-with-cn-or-filter

Screenshots or screen recordings

GET CALL

POST CALL