Add token issuer configuration guide documentation

[HasiniSama]

Purpose

$subject

Related Issues:

wso2/product-is#26593

[coderabbitai]

Walkthrough

This PR introduces documentation for configuring custom token issuers in OAuth2. A shared template file is created and included across multiple Identity Server documentation versions (7.0.0, 7.1.0, 7.2.0, and next). Navigation entries are added to each version's mkdocs configuration.

Changes

Cohort / File(s)	Summary
Documentation Includes en/identity-server/7.0.0/docs/.../configure-custom-token-issuer.md, en/identity-server/7.1.0/docs/.../configure-custom-token-issuer.md, en/identity-server/7.2.0/docs/.../configure-custom-token-issuer.md, en/identity-server/next/docs/.../configure-custom-token-issuer.md	Added template include directives to pull shared content from the centralized template file, enabling consistent documentation across versions.
Shared Template en/includes/references/extend/authentication/oauth2/configure-custom-token-issuer.md	New documentation file detailing configuration of default and custom token issuers for OAuth2, including built-in issuers, deployment.toml configuration, custom issuer registration, and examples.
Navigation Configuration en/identity-server/7.0.0/mkdocs.yml, en/identity-server/7.1.0/mkdocs.yml, en/identity-server/7.2.0/mkdocs.yml, en/identity-server/next/mkdocs.yml	Added navigation entries under OAuth2 section linking to the custom token issuer configuration documentation in each version.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 In documentation fields so wide,
Custom token issuers shall reside,
With template shared across all versions bright,
Navigation guides lead readers right,
OAuth2's path made clear and clear! 🌟

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The PR description lacks required sections and provides minimal meaningful content—only a placeholder subject variable and issue links, with no actual problem description, test environment details, or security checks.	Complete the description by: (1) providing an actual purpose statement replacing '$subject', (2) listing test environments (JDK versions, OS, databases, browsers), and (3) confirming all three security check items.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Add token issuer configuration guide documentation' directly and accurately summarizes the main change: adding documentation for configuring custom token issuers across multiple documentation versions.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into master

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

🧹 Nitpick comments (1)

en/includes/references/extend/authentication/oauth2/configure-custom-token-issuer.md (1)

108-115: TOML snippet may confuse readers — mixing table array and table in one block.

The snippet registers a token type via [[oauth.extensions.token_types]] and then sets [oauth.extensions] in the same code block. In deployment.toml, these are separate sections and their ordering/placement matters. Consider adding a brief note that [oauth.extensions] should appear separately (or before the table array entries) in the file, or split them into two distinct snippets to avoid misconfiguration.