build: upgrade go version to 1.20

[georgehao]

Purpose or design rationale of this PR

Describe your change. Make sure to answer these three questions: What does this PR do? Why does it do it? How does it do it?

1. update the contribute docs
2. update the format tool
3. delete l2geth submodule

PR title

Your PR title must follow conventional commits (as we are doing squash merge for each PR), so it must start with one of the following types:

• build: Changes that affect the build system or external dependencies (example scopes: yarn, eslint, typescript)
• ci: Changes to our CI configuration files and scripts (example scopes: vercel, github, cypress)
• docs: Documentation-only changes
• feat: A new feature
• fix: A bug fix
• perf: A code change that improves performance
• refactor: A code change that doesn't fix a bug, or add a feature, or improves performance
• style: Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc)
• test: Adding missing tests or correcting existing tests

Deployment tag versioning

Has tag in common/version.go been updated or have you added bump-version label to this PR?

• No, this PR doesn't involve a new deployment, git tag, docker image tag
• Yes

Breaking change label

Does this PR have the breaking-change label?

• No, this PR is not a breaking change
• Yes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (566fb23) 48.04% compared to head (e8c25fb) 48.04%.
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1045   +/-   ##
========================================
  Coverage    48.04%   48.04%           
========================================
  Files          101      101           
  Lines        10697    10697           
========================================
  Hits          5139     5139           
  Misses        5128     5128           
  Partials       430      430           

Flag	Coverage Δ
bridge-history-api	11.11% <ø> (ø)
common	55.05% <ø> (ø)
coordinator	18.91% <ø> (ø)
database	42.85% <ø> (ø)
prover	27.32% <ø> (ø)
rollup	66.00% <ø> (ø)

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[colinlyguo]

lgtm