HBASE-26962 Add mob info in web UI (#4359)

[liuxiaocs7]

• cherry-pick from 7a02cbf for branch-2
• see: HBASE-26962

  create 'ui_mob_verify',
    {NAME => 'f1'},
    {NAME => 'f2', IS_MOB => true, MOB_THRESHOLD => 1}

  describe 'ui_mob_verify'

  put 'ui_mob_verify', 'r1', 'f1:q1', 'normal-data-001'
  put 'ui_mob_verify', 'r1', 'f2:q1', 'mob-data-001'
  put 'ui_mob_verify', 'r2', 'f1:q1', 'normal-data-002'
  put 'ui_mob_verify', 'r2', 'f2:q1', 'mob-data-002'

  flush 'ui_mob_verify'

  scan 'ui_mob_verify', {COLUMNS => ['f1:q1', 'f2:q1']}

[Copilot]

Pull request overview

Cherry-pick of HBASE-26962 that surfaces MOB file information on the regionserver per-region web UI page. For mob-enabled column families, the region.jsp page now lists the MOB files referenced by each store file with their size and modification time, and links each to the existing storeFile.jsp viewer.

Changes:

• Adds new imports needed for filesystem, MOB utilities, and URL encoding.
• After the existing Store Files table, when the store is an HMobStore, iterates each store file's MOB_FILE_REFS metadata and renders a new "MOB Files" table.
• Wraps the mob-file lookup in a try/catch that prints the exception text into the table on errors.

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[PDavid]

Thanks!