Fix apimdb database scripts for IBM Db2

[SavinduDimal]

Purpose

• $Subject
• Partial Fix for https://github.com/wso2/api-manager/issues/2762
• Update column definitions which were used for primary key as NOT NULL
• Remove additional index creation scripts
• Remove ON UPDATE CASCADE which is not supported by db2
• Change ON DELETE RESTRICT use cases depending on the use case

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 41.74%. Comparing base (e23b99d) to head (3cfb3c3). Report is 41 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #12394 +/- ## ============================================ - Coverage 47.23% 41.74% -5.50% - Complexity 4212 15703 +11491 ============================================ Files 1869 1858 -11 Lines 138118 137596 -522 Branches 19979 19959 -20 ============================================ - Hits 65245 57433 -7812 - Misses 65131 72872 +7741 + Partials 7742 7291 -451 ``` | [Flag](https://app.codecov.io/gh/wso2/carbon-apimgt/pull/12394/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2) | Coverage Δ | | |---|---|---| | [integration_tests](https://app.codecov.io/gh/wso2/carbon-apimgt/pull/12394/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2) | `41.74% <ø> (-0.14%)` | :arrow_down: | | [unit_tests](https://app.codecov.io/gh/wso2/carbon-apimgt/pull/12394/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2#carryforward-flags-in-the-pull-request-comment) to find out more.

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