FINERACT-2668: Stop bulk-import loan-repayment template loading the entire tenant

[oluexpert99]

• Downloading the loan-repayment template (GET /v1/loans/repayments/downloadtemplate) eagerly fetched every
  client (ClientReadPlatformService.retrieveAll(null) applies no LIMIT) and every active loan, embedding them
  as a tenant-wide Clients sheet, a per-loan lookup table and a 3000-row x 5 VLOOKUP block. The cost is
  O(tenant size) -- multi-MB .xls, slow Excel open, and server heap pressure / OOM risk under concurrent
  downloads -- for an operation that is conceptually O(rows entered). The import handler never reads the
  Clients/Offices sheets; it resolves the loan from the typed account number
  (LoanRepaymentImportHandler -> retrieveLoanIdByAccountNumber), so the embedded dataset is discarded at import.
  - Add an optional lean template, selected by a new LookupMode {AUTO, INCLUDE, EXCLUDE}.
  BulkImportWorkbookPopulatorService gains a 5-arg getTemplate(..., LookupMode); the existing 4-arg signature
  becomes a default delegating with AUTO, so all other callers and templates are unchanged.
  - LoansApiResource#getLoanRepaymentTemplate exposes ?includeLookups={true|false}, mapped to a LookupMode
  (null -> AUTO, true -> INCLUDE, false -> EXCLUDE). INCLUDE keeps the previous unbounded behaviour (the caller
  accepts the full cost). EXCLUDE always produces a lean template. AUTO bounds the client/loan fetch with a SQL
  LIMIT and degrades to lean when either set exceeds fineract.bulk-import.template.max-lookup-rows
  (default 10000), surfaced through FineractProperties.
  - LoanRepaymentWorkbookPopulator gains a lean mode (static lean()/full() factories) that omits the
  client/office sheets, the per-loan lookup table and the 3000-row VLOOKUP block, while keeping the data-entry
  column layout intact (the import handler parses by fixed column index) and retaining the payment-type
  dropdown sourced from the small Extras sheet (extracted to a shared addPaymentTypeValidation()).
  - Add unit tests: LookupMode mapping; the max-lookup-rows cap boundary; and lean-mode output asserting the
  Clients/Offices sheets and per-loan lookup rows are omitted while the data-column headers are preserved.

Description

Describe the changes made and why they were made. (Ignore if these details are present on the associated Apache Fineract JIRA ticket.)

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[adamsaghy]

No need for hardcoded value

[adamsaghy]

I am having some concerns... limiting the number of fetched data, limiting the data you got... What if you need all 20k clients or loan? Maybe i dont fully understand this functionality... can you please help me to understand what these templates, downloadTemplates, bulk-import is doing exactly and used for what purpose?