Implemented file manifest generation and relevant testing

[jeff-cohere]

This PR is larger than I wanted it to be, but I guess we're still in the throes of early development.

Points of interest:

• The DTS now gets its own endpoint, which provides access to its local file system. This is reflected in an updated configuration file format
• The DTS now writes a manifest.json file and uses its local endpoint to transfer the manifest to the destination endpoint.
• I've added a "local" endpoint type for testing, since it wasn't clear how to test manifest transfers in CI systems like GitHub Actions. Seems to work!
• Endpoints now have a Root() method in their interface, which tells you the root directory of their underlying file system. This turns out to be very helpful.
• I rearranged the logic a bit in the TaskManager type, bestowing the lifecycle-related stuff upon a "task" type. I hope the flow of control is a little simpler and more resiliant to concurrent requests.

Work still to do (perhaps in later PRs):

• I've spent almost no time on the contents of the manifest. My concern with this PR was allowing the DTS to write a manifest locally and transfer it to the destination endpoint, which required most of the surgery.
• Files are written to a generic "user" directory with the transfer ID (UUID) as a subdirectory. I don't know what we actually want in practice, so this is just a "rock" for us to start complaining about.
• The example config file in the repo is way out of date at this point. This will start to matter pretty soon.
• There's probably some code cleanup that can be done. A good thing for us to discuss.

Closes #29

[codecov[bot]]

Codecov Report

Attention: 68 lines in your changes are missing coverage. Please review.

Comparison is base (44549b0) 71.95% compared to head (b56fb34) 72.84%.

Files	Patch %	Lines
endpoints/local/endpoint.go	72.32%	23 Missing and 8 partials :warning:
core/task_manager.go	90.00%	12 Missing and 2 partials :warning:
services/prototype.go	30.00%	10 Missing and 4 partials :warning:
endpoints/globus/endpoint.go	82.35%	5 Missing and 1 partial :warning:
endpoints/endpoints.go	60.00%	2 Missing :warning:
databases/jdp/jamo.go	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #32 +/- ## ========================================== + Coverage 71.95% 72.84% +0.88% ========================================== Files 12 13 +1 Lines 1405 1609 +204 ========================================== + Hits 1011 1172 +161 - Misses 329 361 +32 - Partials 65 76 +11 ```

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

[jeff-cohere]

Looks like Globus has discontinued support for Globus Connect Server v4 as of December 2023. This PR is affected because we test our Globus endpoints with some GCSv4 servers that had been made available by Globus for tutorial purposes but no longer seem to work (they return an error message saying "GCSv4 is no longer supported. Contact your sysadmin.").

I'll try to figure out another way to test our basic Globus endpoint features. We're going to be dealing with these kinds of externalities with DTS throughout the project, so minimizing them is worthwhile in any case.