### What changes were proposed in this pull request?
Introduce `configuration.md` to document dynamic config and config service.
### Why are the changes needed?
`DynamicConfig` and `ConfigService` have already been supported in #2100, which should be documented to introduce the feature.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
No.
Closes#2336 from SteNicholas/CELEBORN-1286.
Authored-by: SteNicholas <programgeek@163.com>
Signed-off-by: SteNicholas <programgeek@163.com>
