[Proposal] Ignoring properties for Insert or Update (Dapper.Contrib)

There are now Write and Computed attributes
Properties with those attributes are ignored in both Insert and Update methods.

We have use case now where we want some properties to be ignored on insert, but not on update, or vice-versa.

For example, DateCreated and DateModified.
On insert we want database to generate these dates. These columns have default getdate() constraints and after insert both DateCreated and DateModified will be the same.
DateCreated will obviously never change, but DateModified will change in application and be updated in database.

Now only DateCreated has Computed attribute which means we set DateModified in code and insert it into table. Since we set it to DateTime.Now, DateCreated is later than DateModified, which is not so good.

I think it would be convenient if there is a new attribute, someting like "IgnoreInsert" or similar, for ignoring properties for insert.
And maybe introduce new attribute, "IgnoreUpdate", and those two could maybe replace Write and Computed attributes after some time.

If there is interest, I myself could implement it and send pull request.
What do you think?

Start by reviewing the existing Write and Computed attributes and the Insert and Update methods in Dapper.Contrib. Clarify whether separate IgnoreInsert and IgnoreUpdate attributes should replace or coexist with the current attributes, using the DateCreated and DateModified example as the acceptance case. Done means the intended per-operation property behavior is specified and implemented consistently.