Improve ADOT and IRSA docs: automate RBAC, dedicated ServiceAccounts

[snarkychef]

Issue #, if available:
Fixes https://github.com/aws/eks-anywhere-internal/issues/3712
Fixes https://github.com/aws/eks-anywhere-internal/issues/3536

Description of changes:

- Replaces inappropriate `pod-identity-webhook` ServiceAccount reuse with dedicated ServiceAccount per package
- Eliminates manual ClusterRole/ClusterRoleBinding creation via automated helm chart features (presets or explicit rules)
- Adds both simplified (preset-based) and advanced (explicit rules) configuration examples
- Updates IRSA guidance to reference dedicated ServiceAccounts

Changes align with official AWS EKS ADOT addon best practices and match existing E2E test implementations. RBAC resources are now managed as part of the package lifecycle, eliminating orphaned resources and manual maintenance overhead.

Testing (if applicable):

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.56%. Comparing base (7c47a0b) to head (54df845).

Additional details and impacted files

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##             main   #10414   +/-   ##
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  Coverage   69.56%   69.56%           
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  Files         670      670           
  Lines       40676    40676           
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  Hits        28297    28297           
  Misses      10670    10670           
  Partials     1709     1709           

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