Duplicate metatag settings error

Problem/Motivation

The `social_metatag` module overwrote settings for the metatag module by
adding a duplicate config file in `config/install`. This works when all
modules are installed during site-install, and it also worked in the era
of features. However sites extending Open Social might install the
`metatag` module first and then want the Open Social defaults from
`social_metatag` which will cause a duplicate config error.

Steps to reproduce

Proposed resolution

Moving the configuration to config/modify will properly update the
settings on install without having duplicated config.

Remaining tasks

User interface changes

API changes

Data model changes