[DOCS] Reformat index API documentation

[jrodewig]

Where possible, we should standardize our index API documentation to match the Elastic API reference template.

Relates to elastic/docs#937.

Index APIs to rewrite

• Create Index ([DOCS] Reformat create index API docs #45749)
• Delete Index ([DOCS] Reformat delete index API docs #45755)
• Get Index ([DOCS] Reformat get index API docs #45758)
• Indices Exists ([DOCS] Reformat indices exists API docs #45918)
• Close Index API ([DOCS] Separate and reformat close index API docs #45922)
• Open Index API ([DOCS] Reformat open index API docs #45921)
• Shrink Index ([DOCS] Reformat shrink index API docs #46711)
• Split Index ([DOCS] Reformat split index API docs #46713)
• Rollover Index ([DOCS] Reformat rollover index API docs #46778)
• Clone Index ([DOCS] Reformat clone index API docs #46762)
• Put Mapping ([DOCS] Reformat put mapping API docs #45709)
• Get Mapping ([DOCS] Reformat get mapping API. Reformat and reuse multi-index params. #45699)
• Get Field Mapping ([DOCS] Reformat get field mapping API docs #45700)
• Types Exists ([DOCS] Reformat type exists API docs #47601)
• Add index alias ([DOCS] Separate add index alias API docs #46086)
• Delete index alias ([DOCS] Add delete index alias API docs #46080)
• Get index alias ([DOCS] Add get index alias API docs #46046)
• Index alias exists ([DOCS] Add index alias exists API docs #46042)
• Update index alias ([DOCS] Reformat update index aliases API docs #46093)
• Update Indices Settings ([DOCS] Reformat update index settings API docs #45931)
• Get Settings ([DOCS] Reformat get index settings API docs #45924)
• Analyze ([DOCS] Reformats analyze API #45986)
• Put index template ([DOCS] Reformat "put index template" API docs #46297)
• Delete index template ([DOCS] Add "delete index template" API docs #46101)
• Get index template ([DOCS] Add "get index template" API docs #46296)
• Index template exists ([DOCS] Add "index template exists" API docs #46095)
• Indices Stats ([DOCS] Reformat index stats API docs #46322)
• Indices Segments ([DOCS] Reformat index segments API docs #46345)
• Indices Recovery ([DOCS] Reformat index recovery API docs #46493)
• Indices Shard Stores ([DOCS] Reformat index shard stores API docs #46504)
• Clear Cache ([DOCS] Reformat clear cache API docs #46512)
• Flush ([DOCS] Reformat flush API docs #46875)
• Synced flush ([DOCS] Separate and reformat synced flush API docs #46634)
• Refresh ([DOCS] Separate and reformat synced flush API docs #46634)
• Force Merge ([DOCS] Reformat force merge API docs #46685)

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