Task persistence and a reorganized task manager

[jeff-cohere]

The main purposes of this PR is to teach the DTS how to save and restore tasks when it is stopped and restarted. This objective, combined with the goal of keeping it relatively easy to add new database/endpoint implementations (and test fixtures for both) required me to rethink how things are organized a bit. The biggest changes are:

• The task manager has been pulled out of the core package and given its own tasks package
• The task manager is now a singleton, and there's no longer an accessible object instance for it, because the singleton pattern done the OO way is a rat's nest! Instead, there are functions namespaced by the tasks package for doing the needful.
• The task manager now leverages information in the config file, since it's no longer considered to be a "core" thing. This makes it easier to get data about the system as a whole.
• Logic has been cleaned up and reworked as needed in the databases and endpoints packages.

Additionally, I've reworked the example configuration file.

Closes #34 Closes #35

[codecov[bot]]

Codecov Report

Attention: 167 lines in your changes are missing coverage. Please review.

Comparison is base (63f6cdb) 61.95% compared to head (1e10656) 61.43%.

Files	Patch %	Lines
tasks/tasks.go	64.39%	101 Missing and 40 partials :warning:
config/config.go	20.00%	6 Missing and 2 partials :warning:
endpoints/endpoints.go	74.19%	6 Missing and 2 partials :warning:
services/prototype.go	38.46%	8 Missing :warning:
databases/databases.go	50.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #40 +/- ## ========================================== - Coverage 61.95% 61.43% -0.52% ========================================== Files 13 12 -1 Lines 1732 1893 +161 ========================================== + Hits 1073 1163 +90 - Misses 527 578 +51 - Partials 132 152 +20 ```

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