Add closeStagingRepositories and releaseStagingRepositories summary tasks (#236)

[Vampire]

Fixes #236

[szpak]

Thanks for your contribution.

I agree that they might be useful. I believe, there was a similar discussion years ago and (AFAIR) the main argument against, given by someone, was increased number of tasks (to quickly understand what should be used for new users) and a chance to (try to) accidentally close "too many" repositories.

While the first one might be some problem for newcomers, more experiences users could be happy having them. In the second case, I think that having 2+ repositories configured requires some "knowledge" about Gradle and people should be aware of the pitfalls.

Wrapping up, I'm ok for that contribution as it is more a matter of taste. @TWiStErRob How do you see it?

Btw, @Vampire it would be good to have them mentioned in README to make people more aware of that "simplification".

[TWiStErRob]

I like lifecycle/convenience tasks if they're well documented, which seems to be the case (descriptions and groups are clear, naming could be improved).

[szpak]

Thanks @Vampire (also for using the textBlock). Rebased with master and force pushed.

@TWiStErRob How do you like it?

[TWiStErRob]

Thanks for your patience, sorry for the wait.

I think it ended being nice and clean. Looks reasonable to me.

These's one final nit: the title of the PR (and therefore the commit on master) needs -ies, right?

[Vampire]

Absolutely, thanks.
Fixed both, commit message and PR title

[szpak]

Thanks again, merged.

Btw, using the merge queue makes it problematic to change the squash commit message :-/