Update release doc with v0.29.0 LTS

[savitaashture]

Changes

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Has Docs if any changes are user facing, including updates to minimum requirements e.g. Kubernetes version bumps
• Has Tests included if any functionality added or changed
• Follows the commit message standard
• Meets the Tekton contributor standards (including functionality, content, code)
• Has a kind label. You can add one by adding a comment on this PR that contains /kind <type>. Valid types are bug, cleanup, design, documentation, feature, flake, misc, question, tep
• Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings). See some examples of good release notes.
• Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

NONE

[khrm]

/lgtm

[khrm]

/approve

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: khrm

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[tekton-robot]

@savitaashture: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-tekton-triggers-unit-tests	7b6d7d0	link	unknown	/test tekton-triggers-unit-tests

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