update endpoint docs

Created by: ima23

Copy of PR https://github.com/Ensembl/ensembl-rest/pull/376 (release/98) now on master

Description

Using one or more sentences, describe in detail the proposed changes.

One more VEP plugin will be available through the VEP endpoint. The documentation in this PR is needed for the plugin. The corresponding parameters config are in PR https://github.com/Ensembl/ensembl-rest_private/pull/61

Use case

Describe the problem. Please provide an example representing the motivation behind the need for having these changes in place.

Plugin functionality available through REST.

live: http://rest.ensembl.org/documentation/info/vep_id_get sandbox: http://ves-hx2-76.ebi.ac.uk:6083/documentation/info/vep_id_get

Benefits

If applicable, describe the advantages the changes will have.

Without this documentation, the endpoint will not display the availability of the functionality in the background.

Possible Drawbacks

If applicable, describe any possible undesirable consequence of the changes.

Testing

Have you added/modified unit tests to test the changes? No tests added. Local test server page checked manually.

If so, do the tests pass/fail? pass

Have you run the entire test suite and no regression was detected? No change to code. Test ran.

Tested : http://hx-noah-74-15:3000/vep/human/id/rs699?content-type=application/json;CADD=1

Changelog

Are you changing the functionality of an endpoint? If so, please give a one line summary for the public facing changelog.

[/vep/:species/hgvs/] new plugin option added: CADD [/vep/:species/id/] new plugin option added: CADD [/vep/:species/region/] new plugin option added: CADD