upload: Don't re-add assignees/reviewers that were removed

[jerry-skydio]

If an assignee/reviewer was removed intentionally, don't re-add them.
Add a --force-reviewers flag to bypass this that defaults to false

[jerry-skydio]

Reviews in this chain:
└#236 upload: Don't re-add assignees/reviewers that were removed
　└#238 upload: Add pr body source argument
　　└#239 test: Add more tests for rebase functionality of upload
　　　└#246 Replace patch-id rebase detection with merge-tree comparison

[jerry-skydio]

#	head	base	diff	date	summary
0	7813d73b	e7e87173	diff	Apr 23 16:44 PM	3 files changed, 55 insertions(+)
1	1b50bf6b	e7e87173	diff	Apr 23 16:44 PM	0 files changed
2	6da080cd	e7e87173	diff	Apr 23 16:47 PM	3 files changed, 18 insertions(+), 13 deletions(-)
3	ae550a62	8ef07d58	rebase	Apr 28 12:17 PM	0 files changed
4	44de8896	9cf38dc9	rebase	Apr 28 12:19 PM	0 files changed
5	00e961df	f7c9d0de	rebase	Apr 28 12:20 PM	0 files changed
6	74f99781	0ef7ecb0	diff	Apr 28 12:33 PM	0 files changed
7	16ba2dc0	0ef7ecb0	diff	Apr 28 12:39 PM	1 file changed, 4 insertions(+), 1 deletion(-)