doc add java instrumentation overhead

[SylvainJuge]

• document performance overhead
• add link in migration guide

[elastic-acrolinx]

Acrolinx Scorecards

Select the total score link to review all feedback on clarity, consistency, tone, brand, terms, spelling, grammar, readability, and inclusive language. You should fix all spelling errors regardless of your total score. Fixing spelling errors helps maintain user trust in overall content quality.

Article	Total score (Required: 80)	Words + phrases (Brand, terms)	Correctness (Spelling, grammar)	Clarity (Readability)
✅ docs/_edot-sdks/java/migration.md	55	27	51	22
✅ docs/_edot-sdks/java/overhead.md	57	20	66	21
✅ docs/_edot-sdks/java/release.md	63	17	9	17

*TBD

[elastic-acrolinx]

Acrolinx Scorecards

Select the total score link to review all feedback on clarity, consistency, tone, brand, terms, spelling, grammar, readability, and inclusive language. You should fix all spelling errors regardless of your total score. Fixing spelling errors helps maintain user trust in overall content quality.

Article	Total score (Required: 80)	Words + phrases (Brand, terms)	Correctness (Spelling, grammar)	Clarity (Readability)
✅ docs/_edot-sdks/java/migration.md	55	27	51	22
✅ docs/_edot-sdks/java/overhead.md	58	21	67	21
✅ docs/_edot-sdks/java/release.md	63	17	9	17

*TBD