Feature: Dynamic repositories detection while processing certain directory

[P0Lx]

In my use case the number of repos in a directory can change over time.

Therefore I need to register them before any mu operation.

A nice solution for that would by a dynamic detection of all repos in certain directory.

For example in the .mu_repo file by adding property like this:

repo=directory\*

Would cause mu-repo first to detect all repositories in the indicated directory, and than execute git operation on it.

[P0Lx]

One level of repositories detection is enough for me, but by adding property

repo=directory\**

can cause deep repo detection.

[fabioz]

@P0Lx are you interested in providing a PR for that?

i.e.: I don't have a use for this myself (and thus I won't be implementing it), but I'm open to a PR implementing it.

[Matt-Soft]

@fabioz @P0Lx I will provide PR for that