Fix Lambda config docs

[t-kikuc]

What this PR does / why we need it:

Fix Lambda config docs in the configuration-reference.
The main changes are:

• Fix field names: UpperCamelCase -> lowerCamelCase
• Fix field names:
  • ImageURI -> image
  • SecurityGroupIDs -> securityGroupIds
  • SubnetIDs -> subnetIds
  • SourceCode -> source [edited in 709ac39]
• Fix Required values and add explanations

For Reviewers

See function.go.

Which issue(s) this PR fixes:

N/A

Does this PR introduce a user-facing change?: no

• How are users affected by this change: no
• Is this breaking change: no
• How to migrate (if breaking change): no

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 22.83%. Comparing base (46b475c) to head (d5a5217).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5087      +/-   ##
==========================================
- Coverage   22.84%   22.83%   -0.01%     
==========================================
  Files         409      409              
  Lines       43300    43300              
==========================================
- Hits         9891     9889       -2     
- Misses      32630    32633       +3     
+ Partials      779      778       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[khanhtc1202]

nice catch 👍

[Warashi]

👍🏻

[khanhtc1202]

Thx