【Hackathon No.12】add RFC for pairwise_distance API (#165)

* RFC for paddle.nn.functional.pairwise_distance (cattidea#52)

* rfc:pairwise_distance

* v0.1.1:格式修改

* 丰富了Paddle现状

* Update rfcs/APIs/20220705_api_design_for_pairwise_distance.md

Co-authored-by: Nyakku Shigure <sigure.qaq@gmail.com>

* v 0.1.2

* v 0.1.3

* v 1.0.4

* v 1.0.5

* v1.0.0

Co-authored-by: Nyakku Shigure <sigure.qaq@gmail.com>

* 删除epsilon参数的测试

* 补充实现方案

Co-authored-by: Nyakku Shigure <sigure.qaq@gmail.com>