Add v0.26.x release doc

[khrm]

Changes

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[khrm]

/kind documentation

[savitaashture]

I forgot how we decide LTS for triggers 🤔 is it based on Pipelines LTS ?

[khrm]

Now, it's all LTS. Earlier, we were doing more releases, so release align with Pipelines LTS was LTS.

[khrm]

Deprecate in favour of #1732

[khrm]

/close