TLAB-2169: Updated threat intel documentation to remove references to TAXII2 in manually uploaded indicators

[aj-sumo]

Purpose of this pull request

This pull request replaces the use of "TAXII2" source name in the examples that are not related to TAXII2. The source name being "TAXII2Source" is confusing when the indicators are being uploaded manually (not coming from a TAXII2 source).

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)

TLAB-2169

Test evidence

• Docs render correctly

[cla-bot]

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[jpipkin1]

Looks great, @aj-sumo. Thanks for making the updates!

[jpipkin1]

@aj-sumo, as soon as we get PR #5633 approved, the verification check will pass and we can publish the PR.