[Tizen6.5 Migration][Service] Add getPkgApiVersion for global model

[Tizen6.5 Migration][Service] Add getPkgApiVersion for global model

xwalk.utils.getPkgApiVersion will return required_version of
config.xml. (a.k.a. api version)
This getPkgApiVersion() is used to check api privileges which is
allowed in Tizen platform version.

Without this patch, getPkgApiVersion() will returns wrt-service
package's api version in its manifest.

Reference:
  https://review.tizen.org/gerrit/247389/

Change-Id: Id084f2eda53e3310a2d7c5842d6bd1be4ca34fe0
Signed-off-by: DongHyun Song <dh81.song@samsung.com>