Add GitHub Action to create a new Release with xpi attachment on new tag push

[frazar]

This PR adds a GitHub action that, every time a tag is pushed, will create a new Release with the .xpi attached. The Release will have an automatically-generated changelog with the short log of all commits since the previous release. Additionally, the associated .xpi file will be attached to the Release.

For a preview of the final result, check out the Releases page of my fork.

Note that, for the GitHub action to work, read and write permissions must be granted. This can be done in Settings > Actions > General > Workflow permissions and choosing Read and write permissions.

[jeevatkm]

@frazar Thanks for your PR.
I have tried the xpi from the https://github.com/frazar/ReplyWithHeaderMozilla/releases, it is not working with TB. May be we have to check the packaging. This release I will make it as before. I will get back to your back to PR.

[frazar]

I see. It seemed to be working on my installation though. Maybe some issue with the signing of the package?
What exactly is the set of commands you use for creating the package?

[jeevatkm]

I typically do one line command -

zip -r replywithheader-v<semver-here>.xpi * -x ".*"

I think we do not need Makefile approach, GitHub actions are good to enough to run shell commands to package and publish.