fix: object_store config

[jiacai2050]

Which issue does this PR close?

Closes #

Rationale for this change

After #421, config of object store is changed, but minimal config is still using old format, and it will cause error below

thread 'main' panicked at 'Failed to parse config.: ParseToml { path: "/etc/ceresdb/ceresdb.toml", source: Error { inner: ErrorInner { kind: Custom, l
ine: Some(21), col: 0, at: Some(381), message: "missing field `mem_cache_capacity`", key: ["analytic", "storage"] } }, backtrace: Backtrace(   0: <sna

What changes are included in this PR?

Are there any user-facing changes?

No

How does this change test

CI

[ZuLiangWang]

LGTM