Add support for schema validators

[kevin-bates]

This pull request adds support for schema validators after learning that the default validate() method in jsonschema can leak memory when called repeatedly. (See #2826 for details)

Aside from using the Draft7Validator by default, we also expose the ability for SchemasProvider implementors to bring their own validators as part of their provider.

Rather than create a validator instance whenever validation is required (as was done in the results for #2826), the SchemaManager captures the validator's instance upon loading the SchemasProvider. By doing this, the overall test time went from 16 seconds to 2 seconds, thereby gaining an overall 50X performance improvement over using the default validate() method done originally.

Resolves: #2826

Developer's Certificate of Origin 1.1

   By making a contribution to this project, I certify that:

   (a) The contribution was created in whole or in part by me and I
       have the right to submit it under the Apache License 2.0; or

   (b) The contribution is based upon previous work that, to the best
       of my knowledge, is covered under an appropriate open source
       license and I have the right under that license to submit that
       work with modifications, whether created in whole or in part
       by me, under the same open source license (unless I am
       permitted to submit under a different license), as indicated
       in the file; or

   (c) The contribution was provided directly to me by some other
       person who certified (a), (b) or (c) and I have not modified
       it.

   (d) I understand and agree that this project and the contribution
       are public and that a record of the contribution (including all
       personal information I submit with it, including my sign-off) is
       maintained indefinitely and may be redistributed consistent with
       this project or the open source license(s) involved.

[elyra-bot]

Thanks for making a pull request to Elyra!

To try out this branch on binder, follow this link:

[kiersten-stokes]

Good idea to allow custom validators - everything is working well for me!