[Release] Correctly translate contributors name in release notes

This commit involves three main changes:

(1) It separates the translation of contributor names from the
generation of the contributors list. This is largely motivated
by the Github API limit; even if we exceed this limit, we should
at least be able to proceed manually as before. This is why the
translation logic is abstracted into its own script
translate-contributors.py.

(2) When we look for candidate replacements for invalid author
names, we should look for the assignees of the associated JIRAs
too. As a result, the intermediate file must keep track of these.

(3) This provides an interactive mode with which the user can
sit at the terminal and manually pick the candidate replacement
that he/she thinks makes the most sense. As before, there is a
non-interactive mode that picks the first candidate that the
script considers "valid."

TODO: We should have a known_contributors file that stores
known mappings so we don't have to go through all of this
translation every time. This is also valuable because some
contributors simply cannot be automatically translated.

Conflicts:
	.gitignore