Changes

chore (tiflash): Libclara support (1) (#3471)

This PR makes CI in https://github.com/pingcap/tiflash/pull/10081
compile:

1. Use -v2 image
([source](https://github.com/pingcap/tiflash/pull/10096)), which now
supports dev tools used by CI, and protobuf-compiler required by TiFlash
libclara
2. Mount libclara-cache directory
3. Utilize libclara-cache in PR build, and build libclara-cache after PR
is merged.

A working CI to compile with libclara is:
https://do.pingcap.net/jenkins/blue/organizations/jenkins/pingcap%2Ftiflash%2Fpull_unit_test/detail/pull_unit_test/4044/pipeline

However due to libclara PR is not merged, the cache is not available
yet.

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Signed-off-by: Wish <breezewish@outlook.com>
 (commit: a6edaff)