Allow specification of custom artifact glob in @typechain/hardhat

Currently the glob to match build artifacts for which to generate types is hardcoded [here](https://github.com/dethcrypto/TypeChain/blob/92faf28a91fa17a6cb9c34bd29ea9b2cae5d57b3/packages/hardhat/src/index.ts#L69).

While the user can specify additional globs for "externalArtifacts" there is no way to disable type generation for selected contracts/artifacts.
One example where this is a problem is, if the user has multiple contracts with the same name which leads to `Duplicate Identifier` typescript errors.

Adding an optional config parameter to change the hardcoded glob (with the current pattern as the default) would fix this issue.