docs(techniques/authentication): add refresh-token implementation steps

[dinuka-rp]

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] The commit message follows our guidelines: https://github.com/nestjs/docs.nestjs.com/blob/master/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] Other... Please describe:

What is the current behavior?

https://github.com/nestjs/jwt/issues/122

Issue Number:

What is the new behavior?

Add documentation for refresh-token mechanism.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

This NodeJS refresh-token implementation was used as reference to come up with the following refresh-token mechanism for NestJS.

[adamwdennis]

Thanks for this.. It took me a full day to find this answer to my problem with access/refresh tokens... i started by adding a custom claim 'token_type', but this makes SO much more sense (signing refresh tokens with different secrets). Thank you.