[hook] add support to invoke inline functions as hooks

This commit adds support to specify inline functions as meta controller hooks. In other words, meta controller code as well as hook implementation can be built as a single binary. This avoids the need to have http service based invocations i.e. webhooks.

In addition to inline hook support, this commit has following changes:

code refactor w.r.t hook invocation
a new integration test case that showcases use of inline hook

NOTE: This support is also enabled for GenericController. Once this proves to be useful, it may be extended to other meta controllers.

Signed-off-by: AmitKumarDas amit.das@mayadata.io

AmitKumarDas / metac

[hook] add support to invoke inline functions as hooks #36