fix(boilingcore): use conventional camelCase for struct tag casing

[KeitaShimura]

Summary

When json = "camel" (or any tag format set to camel) is configured, SQLBoiler
was using strmangle.CamelCase which follows Go's initialism convention. This
caused column names like account_id to be rendered as accountID in struct
tags, whereas the conventional camelCase for JSON APIs is accountId.

This PR introduces camelCaseNoInitialisms in boilingcore/templates.go and
uses it in generateTagWithCase for TagCaseCamel instead of
strmangle.CamelCase.

Changes

• boilingcore/templates.go: Add camelCaseNoInitialisms which converts
  snake_case to camelCase by title-casing only the first letter of each word,
  without uppercasing common Go initialisms (e.g. ID, URL). Update
  generateTagWithCase to use this function for TagCaseCamel.
• boilingcore/templates_test.go: Add TestCamelCaseNoInitialisms and
  TestGenerateTagWithCaseCamel to verify the new behaviour.

Behaviour change

Column name	Before (broken)	After (fixed)
account_id	accountID	accountId
http_url	httpURL	httpUrl
column_name_id	columnNameID	columnNameId

Note: This is a breaking change for users who were relying on the previous
(Go-initialism) output. However, the previous output did not conform to JSON
camelCase conventions, so this is considered a bug fix.

Related issue

Related to #1411

[stephenafamo]

This will be a breaking change which is unacceptable