Docs: Record bucket search by item type

[Remington Steed]

The following section of the docs needs to include details about "search_format()" and "item_type()".

http://docs.evergreen-ils.org/dev/_adding_records_to_a_bucket.html

Here are details as provided by Galen via email (https://markmail.org/message/mirpd5rvv7kk5wom):
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One way of limiting the results is to tack on a search_format clause at the end of query. For example

ti:harry potter and the order of the phoenix search_format(electronic)

will limit it to electronic resources

Options for search_format include electronic, playaway, blu-ray, book, cdaudiobook, casaudiobook, dvd, and so forth.

To filter specifically on the Leader/06 value, you can use item_type(). For example,

ti:harry potter and the order of the phoenix item_type(i)

will limit the search to nonmusical sound recordings.

[Britta Dorsey (bdorsey-isl)]

Tested on MOBIUS public server (Version HEAD)

Here is my documentation write-up for this launchpad ticket.

[Andrea Neiman (aneiman)]

Pushed to master - will be backporting after lunch :)

Thank you Britta!

[Andrea Neiman (aneiman)]

Alright! Backported alllll the way to 3.6, thank you Britta again! And secondary thanks to Jeff Godin for git help :)

Did not put LP targets for 3.6-3.8 because they are EOL in a code sense.

[Andrea Neiman (aneiman)]

Realizing that my commit did not include the LP tag (bad committer!) so here's the commit link:
https://git.evergreen-ils.org/?p=Evergreen.git;a=commit;h=093c5f88ac366e96b6c403234632624e21c188a0