Add Rate Limit using Istio Envoy

[joonhyukchoi]

What this PR does / why we need it:
To limit a large number of requests, such as in a DDoS attack, we can use Istio(envoy)'s rate limit in K8s ingress.
Which issue(s) this PR fixes:

Fixes #590

Special notes for your reviewer:
I have tested on local K8s environment with yorkie-cluster Helm chart with minikube, and it worked as expected.
Does this PR introduce a user-facing change?:

Additional documentation:

Checklist:

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5500afb) 48.96% compared to head (49d0686) 48.81%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #674      +/-   ##
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- Coverage   48.96%   48.81%   -0.15%     
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  Files          69       69              
  Lines       10090    10127      +37     
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+ Hits         4941     4944       +3     
- Misses       4631     4657      +26     
- Partials      518      526       +8     

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[krapie]

Thank you for your contribution.
I think it will be good to have the opportunity to demonstrate and explain this feature (on weekly sync or personal meeting).

Leaving two major suggestions below:

1. Since we have many manifests in single directory templates, how about seperating manifests for each service by directory like below?

- templates
  - yorkie
    - deployment.yaml
  - istio
    - ingress.yaml
    - ratelimit.yaml

2. How about adding enable/disable value in values.yaml to enable and disable rate limiting base on their needs?

ratelimit:
  enabled: false

[krapie]

Thank you for applying my feedbacks.
I left few more comments below.

How about setting requestsPerUnit to 10000 for now?

Considering total request metric in #590 and total request metric of this month(2023.11.01 ~ 2023.11.23), I think setting 10000 requests per minute will do.

(total request metric of #590, approximately 10000+ per minute)

(highest total request metric between 2023.11.01 and 2023.11.23, approximately 8000- per minute)

[krapie]

@joonhyukchoi After you finish your revision, please re-request review for further progress.

[krapie]

LGTM! It works perfectly!

FYI, I could not find references that global rate limit is done per source ip (seems like it is default setting in global rate limit). For local rate limit, we can use remote_address key to rate limit per source ip. So we need to check if global rate limit works per source ip after we apply this changes in our cluster.