Refine CI process & Clean internal service links

[solotzg]

Feature Request

Is your feature request related to a problem? Please describe:

Describe the feature you'd like:

• Clean internal service links for preparation about open source TiFlash repo renaming and open source preparation #4019.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

• Under https://github.com/pingcap/tics/tree/master/release-centos7-llvm/scripts, to remove:
  • build-tiflash-ci.sh
  • build-tiflash-ut-coverage.sh
  • fetch-ci-build.sh
  • tiflash-ci-prepare.sh
  • tiflash-ci-finish.sh
  • tiflash-ut-coverage-prepare.sh
  • tiflash-ut-coverage-finish.sh
  • upload-ci-build.sh
  • upload-ut-coverage.sh
  • release-centos7-llvm/scripts/env.sh#L1-L2 Clean useless processes and scripts #4153
• Remove
  • https://github.com/pingcap/tics/tree/master/.ci
  • https://github.com/pingcap/tics/tree/master/deprecated/release-centos7

[solotzg]

@SchrodingerZhu @purelind @zanmato1984 PTAL

[SchrodingerZhu]

related CI/CD changes:

Github:

• Rename tics to tiflash
• remove unused build scripts from all branches

CI:

• use separate build scripts (PR):
  • Build
  • UT
  • IT
• create new CI to maintain build cache
  • multibranch
• allocate area for tiflash specific cache file (/mnt/ci.pingcap.net-nfs/tiflash)
• rename pipelines and trigger
  • Build
  • UT
  • IT
  • Bot PR
• Update Code cache path

CD:

currently, CD still works due to GitHub's forwarding of github.com/pingcap/tics.

• rename product and repo in jenkins template PR
• rename product and repo in PingCAP-QE/ci (no PR yet)
• rename product and repo in other QA stuffs (at Jenkins dashboard)
• refactor multibranch
  • use NFS for cache
  • also use universal pipeline script