Add "tail" feature for an already existing file on eKuiper File Source

[canob]

It is a good idea to add "tail" feature for an already existing file on eKuiper File Source All of the most known Observability/Analytics Collectors, like FluentBit (https://fluentbit.io/), Fluentd (https://www.fluentd.org/), Beats (https://www.elastic.co/beats), NXLog (https://nxlog.co/products/nxlog-community-edition), or Vector.dev (https://vector.dev/), allow to "tail" or "watch" a file for new line additions, to collect them. eKuiper File Source only allow to process the same file again everytime, or to process new files in a folder, but not to "tail" or "watch" an already processed file for new line additions. I think that for similar features, work similar to the most used tools on Internet is a must for a product to grow, and eKuiper has all the features to be a star product, so add that kind of enhancements is really important.