[21790] Add references to new nightly jobs per supported branch in README

[JesusPoderoso]

Description

This PR adds references to new nightly jobs per supported branch in README

This PR is on top of (and should be merge after):

• [21789] Split nightly jobs to one per workflow #5292

@Mergifyio backport 3.0.x 2.14.x 2.10.x 2.6.x

NOTE: references to master should be updated in the backports to the corresponding branch name

Contributor Checklist

• Commit messages follow the project guidelines.
• The code follows the style guidelines of this project.
• N/A Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• N/A Any new/modified methods have been properly documented using Doxygen.
• N/A Any new configuration API has an equivalent XML API (with the corresponding XSD extension)
• N/A Changes are backport compatible: they do NOT break ABI nor change library core behavior.
• N/A Changes are API compatible.
• N/A New feature has been added to the versions.md file (if applicable).
• N/A New feature has been documented/Current behavior is correctly described in the documentation.
• Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• N/A If this is a critical bug fix, backports to the critical-only supported branches have been requested.
• N/A Check CI results: changes do not issue any warning.
• N/A Check CI results: failing tests are unrelated with the changes.

[JesusPoderoso]

@Mergifyio backport 3.0.x 2.14.x 2.10.x 2.6.x

[mergify]

backport 3.0.x 2.14.x 2.10.x 2.6.x

✅ Backports have been created

• #5300 [21790] Add references to new nightly jobs per supported branch in README (backport #5293) has been created for branch 3.0.x
• #5298 [21790] Add references to new nightly jobs per supported branch in README (backport #5293) has been created for branch 2.14.x
• #5299 [21790] Add references to new nightly jobs per supported branch in README (backport #5293) has been created for branch 2.10.x
• #5301 [21790] Add references to new nightly jobs per supported branch in README (backport #5293) has been created for branch 2.6.x