docs: clarify tag search behavior in Jaeger UI (fixes jaegertracing/jaeger#7333)

[chethanac15]

Which problem is this PR solving?
Resolves jaegertracing/jaeger#7333
Users were confused about which tags are searchable in the Jaeger UI, especially when tags are set as arrays (e.g., by some OpenTelemetry SDK configurations). The documentation did not clearly state that only string-valued tags are indexed and searchable.

Description of the changes
-Adds a new section "Tag Search Behavior" to the Jaeger UI documentation.
-Clearly explains that only string-valued tags are indexed and searchable in the UI, and that array-valued tags are not.
-Advises users to ensure important tags (such as request IDs) are set as strings, not arrays, when instrumenting their applications.
-References the related GitHub issue for context.

How was this change tested?
-This is a documentation-only change. The content and formatting were reviewed for clarity and correctness.
-No code, UI, or test changes were required.

Checklist
[x] I have read https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
[x] I have signed all commits
[n/a] I have added unit tests for the new functionality (documentation-only)
[n/a] I have run lint and test steps successfully (documentation-only)

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[yurishkuro]

changes should be made in _dev folders, not concrete versions, so that those changes are sticky for future versions.

and this behavior is probably the same for both v1 and v2, it would make sense to update the v2 docs (v1 is being retired end of this year)

[yurishkuro]

I am not sure this is accurate. If the array tag can be retrieved from db then it was indexed as well, but most likely as a JSON string.

[yurishkuro]

it may be indexed as a JSON string (e.g., '["value"]'

are you just restating what I said or did you validate it? Can you search by a string like that?

[yurishkuro]

I think it's a bug. I don't want to make changes to documentation before we fix the bug. jaegertracing/jaeger#7346

[chethanac15]

Addressed maintainer feedback:

• Moved documentation to v2 dev folder.
• Clarified that array-valued tags may be indexed as JSON strings and how to search for them.
• v1 not updated as it is being retired.

Ready for re-review!

[chethanac15]

@yurishkuro I validated this in a running Jaeger instance. I sent a trace with a tag whose value is an array (serialized as ["value"]). The trace appears in the UI when searching by service, but searching for the tag using array_tag:["value"] returns no results. This confirms that array-valued tags are not searchable in the Jaeger UI, even if they are stored as JSON strings. I will update the documentation to clarify that only string-valued tags are reliably searchable.

[yurishkuro]

Repro jaegertracing/jaeger#7346