Feature request

An interface to improve the accessibility of this tool. The objective of this first iteration is to a simple Local Web UI.

Is your feature request related to a problem? Please describe.
Currently, the instructions to run the validator are long and need a certain technical literacy: download JAR file, open the terminal, navigate to the accurate directory, run a command line with selected parameters, open the report in a JSON viewer.
This is a pain point and even a blocker, for many organizations.

Proposed solution
Recover the work started by @lionel-nj in #421, and build an interface that will act as a Minimum Viable Product that we can build on.
We chose to use Spring Boot because it is community supported, scalable, industry-standard, easy to staff.

Describe alternatives you've considered
Better documentation with images so that users that never used the command line before can use this tool.

Additional context
MobilityData had planned to work a local Web UI in Q1 2022 by recovering the work started in #421.
A Web UI is included in contribution #1088. After reviewing and discussing with @lisaattrillium and @ed-g, MobilityData will continue with the initial plan of building a local Web UI on top of the work started in #421, and we will discuss integrating the amazing work done on the HTML output in this validator.

Acceptance Criteria

• As a user, I can open the local web UI with clear instructions.
• As a user, I can upload my GTFS feed and run the validator by clicking on a button.
• As a user, I can see the results on the Interface in a JSON Viewer.

Not doing

• Providing a hosted Interface. This will come later on.
• Work on the validation results. This will be part of another initiative.

cc @asvechnikov2