Missing Blob input plugin doc missing

[eschabell]

Need a new file for this plugin: https://github.com/fluent/fluent-bit/blob/master/plugins/in_blob/blob.c

Including new entry in Summary.md with file name blob.md.

[eschabell]

More adjustments to this plugin coming and adding request for missing review.

[eschabell]

@alexakreizinger asking for a review on the current PR, but please take a look back at the previous PR noted in this issue?

[alexakreizinger]

thanks for the ping—the changes in #2288 look good to me :) happy to review any future updates as well!