tests: t2206-add-submodule-ignored: ignore=all and add --force tests

tests: t2206-add-submodule-ignored: ignore=all and add --force tests

The tests verify that the submodule behavior is intact and updating the
config with ignore=all also behaves as intended with configuration in
.gitmodules and configuration given on the command line.

The usage of --force is showcased and tested in the test suite.

The test file is added to meson.build for execution.

Signed-off-by: Claus Schneider (Eficode) <claus.schneider@eficode.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>