Improve login.jsp file to handle custom local authenticators

[sadilchamishka]

Purpose

The custom local authenticators can be registered as an extension point and can be added to the applications. When there are multiple options for the application, it doesn't show the custom local authenticators as the existing login.jsp doesn't have that support as it only support the already registered defined local authenticators.

This PR is initiated to provide that support, and the documentation should be improved to guide the developers to provide the custom local authenticator logo image and i18 configs as necessary.

Related Issues

• https://github.com/wso2/product-is/issues/20265

After the fix.

[codecov[bot]]

Codecov Report

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

Project coverage is 31.79%. Comparing base (c1a3705) to head (8f8f890). Report is 1019 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #6889 +/- ## ======================================= Coverage 31.79% 31.79% ======================================= Files 41 41 Lines 890 890 Branches 204 220 +16 ======================================= Hits 283 283 + Misses 607 557 -50 - Partials 0 50 +50 ``` | [Flag](https://app.codecov.io/gh/wso2/identity-apps/pull/6889/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2) | Coverage Δ | | |---|---|---| | [@wso2is/core](https://app.codecov.io/gh/wso2/identity-apps/pull/6889/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2) | `31.79% <ø> (ø)` | | 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. [see 15 files with indirect coverage changes](https://app.codecov.io/gh/wso2/identity-apps/pull/6889/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=wso2)

[wso2-jenkins-bot]

🦋 Changeset detected

The changes in this PR will be included in the next version bump.

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