Add clear method implementation

[esc5221]

• Implemented Cache.clear by deleting all items in dynamodb table
• Add test for implemented clear method

Ref : https://gist.github.com/Swalloow/9966d576a9aafff482eef6b59c222baa

[xncbf]

Thanks for the first PR 😄 The reason I haven't implemented the clear method yet is because the cost of using scan is too high. As you knows, as the number of rows increases, the scan cost may increase.

I've been thinking about how to empty the entire row without using scan , but I haven't found one yet. Is there a better way?

[esc5221]

Oh I see.. I didn't considered the high cost of scanning operation. But, isn't it better to have clear method implemented? Implementation may not be the best, but i think it is better than not having it at all. Users can use with their own risk.

Another option that i found was deleting the table and creating it again. But deleting the existing resource seems to be not quite right, so i choose to delete items without deleting the table. How do you think about this option?

[xncbf]

Dropping and recreating tables can take a long time also.

I agree with better than not having it at all. So, let me notify the user of the risk and leave it as a possibility for future improvement.

[xncbf]

Can you give an editing permission?

[esc5221]

It's already enabled. Is there any other settings should i check?

[xncbf]

I don't know why pipelines failed All tests pass on my local env, so after merging we will change dynamodb for testing to sandbox.