DOCS-1841 - Reorder Search Job API sections and make session timeout common

[JV0812]

Purpose of this pull request

Small follow-up to #7080 (same ticket):

• Reorders the two API sections in `docs/api/search-job.md` so Search Job Management API comes before Legacy Search Job API (recommended version first).
• Moves the general session-timeout/keepalive behavior (poll every 20-30s, 8-hour query timeout, async paging) into the shared/common section, since it applies to both versions. Only the cookie-specific requirement (enable cookies, 404 on missing cookie) stays scoped to the Legacy API section.

Verified via `yarn build` (no broken links/anchors).

Select the type of change

• Minor Changes - Typos, formatting, slight revisions
• Update Content - Revisions, updating sections
• New Content - New features, sections, pages, tutorials
• Site and Tools - .clabot, version updates, maintenance, dependencies, new packages for the site (Docusaurus, Gatsby, React, etc.)

Ticket (if applicable)

https://sumologic.atlassian.net/browse/DOCS-1841

[amee-sumo]

Reviewed the full diff — clean follow-up, no issues.

Verified:

• New heading order (shared sections → Search Job Management API → Legacy Search Job API) is logical and now matches the intro's two-bullet comparison at the top of the doc, which already listed Search Job Management API first.
• No content lost in the session-timeout consolidation — the old two-bullet "404 causes" list (cookies disabled / session canceled) is fully covered by the new shared section's cancellation sentence plus the Legacy-scoped :::note on cookies.
• Anchor stability holds: #session-timeout slugs the same whether it's an ## or ### heading, so none of the cross-file links from other docs/blog posts break.
• Admonition fences (the :::tip with the nested MSSP parameter table) are intact after the section move.

One non-blocking note: generalizing the "poll every 20-30s or it's canceled" behavior to also apply to the new Search Job Management API (previously scoped to Legacy only) is a behavioral claim I can't independently verify from the docs alone — flagging only so it's confirmed against the actual API behavior before merge, since it's a slight expansion of scope from what #7080 stated.

[JV0812]

Re the non-blocking note on the poll-every-20-30s behavior applying to both versions — confirmed intentional by the doc owner; the keepalive/inactivity-cancellation behavior is common to both the Legacy API and the Search Job Management API, only the cookie mechanism is Legacy-specific. No content change needed.