[Dashboard] http route handler cache

[fyrestone]

Why are these changes needed?

• Problem
  • The new dashboard needs a cache to avoid unnecessary calculation.
• Solution
  • An aiohttp_cache decorator for aiohttp route handler.
    • If the same request arrives in TTL, just return the cached data.
    • If a new request arrives or the TTL is expired, schedule the http route handler to update cache, and return the cached data.
    • Fixed size with LRU replacement policy, default is 128 (same as functools.lru_cache 's default maxsize).
    • An environment var RAY_DASHBOARD_NO_CACHE(set before the new dashboard starts) to disable cache.
• Other
  • Make the rest_response a normal function (same as aiohttp.web.json_response) instead of an async function.

Related issue number

Closes #10771

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[rkooo567]

@fyrestone Btw, do you mind writing simple documentation about our dashboard framework (like basic how this works and how to use it)? It'll be helpful for future developers who will work on the dashboard. FUN FACT: I also am not familiar how the whole thing works...

[fyrestone]

@fyrestone Btw, do you mind writing simple documentation about our dashboard framework (like basic how this works and how to use it)? It'll be helpful for future developers who will work on the dashboard. FUN FACT: I also am not familiar how the whole thing works...

OK. I will write a document about the new dashboard framework.

[rkooo567]

cc @mfitton Please review the PR!

[rkooo567]

@fyrestone Please resolve the merge conflict!

[fyrestone]

@fyrestone Please resolve the merge conflict!

Thanks. The conflict has been resolved.