feat: support mask_inner and mask_outer

[Azusain]

No description provided.

[ecmadao]

And we can use the RangeMask to define the masker just same as the InnerOuterMask, so I'm not sure its scenario.
Also, the InnerOuterMask cannot define an algorithm to mask the prefix and suffix at the same time, but the RangeMask can do.

[h3n4l]

Also, the InnerOuterMask cannot define an algorithm to mask the prefix and suffix at the same time, but the RangeMask can do.

IMO, use mask outer can do this:
mysql> SELECT mask_outer('This is a string', 5, 1);
+--------------------------------------+
| mask_outer('This is a string', 5, 1) |
+--------------------------------------+
| XXXXXis a strinX |
+--------------------------------------+

https://dev.mysql.com/doc/refman/5.7/en/data-masking-usage.html

[ecmadao]

The proto LGTM

[rebelice]

LG, otherwise

[h3n4l]

LGTM