Change names following #362

[ponyisi]

• SignedURLs -> URLs
• Users specify "root-ttree" instead of "root-file" and enum names are changed to "root_ttree". This involves splitting the types ResultFormat and OutputFormatEnum : the latter is now used in the ServiceXSpec and is translated to a ResultFormat when creating the actual request, so that the string sent to the server is still root-file.

Important Note: The ResultFormat is still what you get back from the server, though, so the cache will continue to handle root-file and not root-ttree. If at some point we change this string it'll have the side-effect of invalidating caches.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.61%. Comparing base (07b7296) to head (bed3d0f). Report is 1 commits behind head on 3.0_develop.

Files with missing lines	Patch %	Lines
servicex/func_adl/func_adl_dataset.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## 3.0_develop #435 +/- ## =============================================== + Coverage 81.54% 81.61% +0.06% =============================================== Files 26 26 Lines 1349 1354 +5 =============================================== + Hits 1100 1105 +5 Misses 249 249 ``` | [Flag](https://app.codecov.io/gh/ssl-hep/ServiceX_frontend/pull/435/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ssl-hep) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/ssl-hep/ServiceX_frontend/pull/435/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ssl-hep) | `81.61% <92.30%> (+0.06%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ssl-hep#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[ponyisi]

Hold off on a merge, I'm trying to fix something...

[ponyisi]

OK, we can continue. I had to remove the redundant string regex validation in the model definition, because that broke the enum coercion; it should be OK because the allowed enum values provide the validation.