rename tinykv example to matrixkv example

[mind1949]

What type of PR is this?

• [ ] API-change
• [ ] BUG
• [ ] Improvement
• [x] Documentation
• [ ] Feature
• [ ] Test and CI
• [ ] Code Refactoring

Which issue(s) this PR fixes:

Fixes #

What this PR does / why we need it:

Not Available

Special notes for your reviewer:

Not Available

Additional documentation (e.g. design docs, usage docs, etc.):

Not Available