Update caching example conforming to the new cache-manager-redis-store interface

[dabroek]

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

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

Other information

Solution as described by the author here.

[kamilmysliwiec]

Apologies for not looking at this PR sooner. There are some new conflicts, could you take a look?

[nopitown]

Is there a plan to merge this soon? The documentation is a bit misleading with the latest updates. Thank you.