Improve support for writing cache files from client

In order to assist users in transitioning their workflows to use condor file transfer, we should attempt to improve support for writing cache files directly in the client library.

It would be great to have something like this (pseudocode):

from os.path import basename
from gwdatafind import find_urls
from gwdatafind.io import LalCache

# find input data OSDF URls
urls = find_urls("H", "H1_HOFT_C00", start, end, urltype="osdf")

# create LAL of basenames for EP
epcache = LalCache(map(basename, urls))
epcache.write("cache.txt")

# write condor job
condor_submit.write(f"arguments = --cache-file=./cache.txt")
condor_submit.write(f"transfer_input_files = {','.join(urls)},cache.txt")

The only thing missing right now is the LalCache object. What would work today to write a names-only LAL-format cache file is:

from gwdatafind.io import lal_cache
with open("cache.txt", "w") as cache_file:
    for line in lal_cache(map(basename, urls)):
        print(line, file=cache_file)

So, the action for this ticket might just be to document this snippet properly on the client docs pages.

added gwdatafind.io label

changed milestone to %GWDataFind Client 1.3.0

mentioned in merge request !102