chore: upgrade to client-go 0.26 etc

[blakepettersson]

This requires argoproj/gitops-engine#537. This builds upon #13965,
with the difference that this does not require any changes in the usage
of managedNamespaceMetadata.

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Toolchain Guide
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
• Optional. My organization is added to USERS.md.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.

[codecov]

Codecov Report

Patch coverage: 47.56% and project coverage change: -0.01% ⚠️

Comparison is base (6ca2e90) 49.90% compared to head (9935047) 49.89%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #15103      +/-   ##
==========================================
- Coverage   49.90%   49.89%   -0.01%     
==========================================
  Files         262      262              
  Lines       45130    45171      +41     
==========================================
+ Hits        22521    22540      +19     
- Misses      20393    20404      +11     
- Partials     2216     2227      +11     

Files Changed	Coverage Δ
applicationset/utils/clusterUtils.go	68.33% <0.00%> (ø)
cmd/argocd/commands/admin/cluster.go	0.00% <0.00%> (ø)
cmd/util/project.go	12.14% <0.00%> (ø)
server/application/terminal.go	12.44% <0.00%> (ø)
util/db/cluster.go	59.23% <0.00%> (ø)
util/db/helmrepository.go	0.00% <0.00%> (ø)
util/db/secrets.go	79.04% <25.00%> (-2.51%)	⬇️
util/rbac/rbac.go	78.77% <25.00%> (-0.77%)	⬇️
util/settings/settings.go	50.14% <25.00%> (-0.49%)	⬇️
cmd/argocd/commands/app.go	21.75% <33.33%> (ø)
... and 5 more

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