Share expiration

[C0rby]

Shares can have an expiration timestamp. If they are accessed after the expiration, the share will automatically be removed.

Todo:

• remove replace and update go-cs3apis, requires: Share expiration cs3apis#192

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[butonic]

I see the ISO8601 pain, the updatemask introduction which causes changes in all implementations and the cs3api replacement. All of which we can address in subsequent PRs. Good to go!