otelconf: add unmarshaling / validation for batch processors

[codeboten]

Follow up to #8043, adds unmarshaling for batch processors. Will rebase once #8043 is merged

Part of breaking up #8026

[codecov]

Codecov Report

❌ Patch coverage is 92.76018% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.8%. Comparing base (4f838f7) to head (2eb2650).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
otelconf/config_common.go	81.8%	6 Missing and 2 partials ⚠️
otelconf/config_json.go	94.4%	3 Missing and 3 partials ⚠️
otelconf/config_yaml.go	97.1%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #8049     +/-   ##
=======================================
+ Coverage   79.7%   79.8%   +0.1%     
=======================================
  Files        190     190             
  Lines      11919   12136    +217     
=======================================
+ Hits        9502    9692    +190     
- Misses      2062    2083     +21     
- Partials     355     361      +6     

Files with missing lines	Coverage Δ
otelconf/config_yaml.go	97.6% <97.1%> (-2.4%)	⬇️
otelconf/config_json.go	95.1% <94.4%> (-4.9%)	⬇️
otelconf/config_common.go	86.2% <81.8%> (-4.5%)	⬇️

... and 1 file with indirect coverage changes

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[codeboten]

Thanks for the suggestions @MrAlias, applied the suggestions PTAL

[MrAlias]

LGTM. Only one small nit.