feat(auto update): add script to decide update method

- hook to be called when auto updating.
- it may be overridden by build.sh

Signed-off-by: Aditya Alok <dev.aditya.alok@gmail.com>

scripts/updates/termux_pkg_auto_update.sh

@@ -0,0 +1,44 @@
+# shellcheck shell=bash
+termux_pkg_auto_update() {
+	local project_host
+	project_host="$(echo "${TERMUX_PKG_SRCURL}" | cut -d"/" -f3)"
+
+	if [[ -z "${TERMUX_PKG_UPDATE_METHOD}" ]]; then
+		if [[ "${project_host}" == "github.com" ]]; then
+			TERMUX_PKG_UPDATE_METHOD="github"
+		elif [[ "${project_host}" == "gitlab.com" ]]; then
+			TERMUX_PKG_UPDATE_METHOD="gitlab"
+		else
+			TERMUX_PKG_UPDATE_METHOD="repology"
+		fi
+	fi
+
+	local _err_msg="ERROR: source url's hostname is not ${TERMUX_PKG_UPDATE_METHOD}.com, but has been
+configured to use ${TERMUX_PKG_UPDATE_METHOD}'s method."
+
+	case "${TERMUX_PKG_UPDATE_METHOD}" in
+	github)
+		if [[ "${project_host}" != "${TERMUX_PKG_UPDATE_METHOD}.com" ]]; then
+			termux_error_exit "${_err_msg}"
+		else
+			termux_github_auto_update
+		fi
+		;;
+	gitlab)
+		if [[ "${project_host}" != "${TERMUX_PKG_UPDATE_METHOD}.com" ]]; then
+			termux_error_exit "${_err_msg}"
+		else
+			termux_gitlab_auto_update
+		fi
+		;;
+	repology)
+		termux_repology_auto_update
+		;;
+	*)
+		termux_error_exit <<-EndOfError
+			ERROR: wrong value '${TERMUX_PKG_UPDATE_METHOD}' for TERMUX_PKG_UPDATE_METHOD.
+			Can be 'github', 'gitlab' or 'repology'
+		EndOfError
+		;;
+	esac
+}