jenkins - gitparam jobdsl - branchFilter
This is how I did:
gitParameter {
            // The name of the parameter.
            name('SELECTED_BRANCH')
            // The type of the list of parameters: Tag - list of all commit tags in repository - returns Tag Name Branch - list of all branch in repository - returns Branch Name Revision - list of all revision sha1 in repository followed by its author and date - returns Tag SHA1
            type('PT_BRANCH')
            // In my case this is a variable pointing to the gitlab hook variable
            defaultValue('$gitlabAfter')
            // A description that will be shown to the user later.
            description('Select a git the configuration you want to deploy')
            // Name of branch to look in.
            branch('')
            // Regex used to filter displayed branches.
            // Whatever is captured in the group will be the name used as the value of the SELECTED_BRANCH
            branchFilter('origin/(config\\/.*)')
            // This parameter is used to get tag from git.
            tagFilter('*')
            // Select how to sort the downloaded parameters.
            sortMode('NONE')
            // Which value is selected, after loaded parameters.
            selectedValue('NONE')
            // If in the task are defined multiple repositories, this option specifies which the repository is taken into account on getting data.
            useRepository(&quot;&lt;my git url&gt;.*&quot;)
            // When this option is enabled will show a text field.
            quickFilterEnabled(false)
            // Specify the number of items the list will display.
            // listSize(String value)
        }


As strange as it seems, some parameters shouldn't really be necessary, but the plugin requires them anyway, so that's why the config is verbose.
Also, pay attention that this one is gitParameter and not gitParam, yes, both exist, and they take different parameters.
For more information about the properties you can go here:
https://plugins.jenkins.io/git-parameter/