add version.txt and github workflow to update file.

[jedwards4b]

add a version.txt file and a --version option to checkout_externals

Adds a pre-push hook to update the file version.txt when you push to the repository.

User interface changes?: Yes
Adds --version option

Fixes: #207

Testing:
test removed:
unit tests: All pass
system tests: All pass
manual testing: ./checkout_externals --version

[jedwards4b]

@erik - this uses a github action added to bumpversion.yml to write the version to a file version.txt on push to main. That file is read by ./checkout_externals --version

[jedwards4b]

I realized that I need to update the version.txt file before generating the tag but I need to get the new tag name before updating the file - this action does that. Tested in https://github.com/jedwards4b/testrepo

[gold2718]

I guess it is okay if it really works. It is a lot harder to try to figure out the new Microsoft TypeScript (:grimacing:) then the first (shell) version.

[gold2718]

Is this going to get cleaned up when it is tagged?
I.s., will it be manic-1.2.25 ?

[jedwards4b]

Yes it will be manic-1.2.25.