fix: remove MeshConfig from ZTunnel CRD

[dgn]

This removes the MeshConfig field from the ZTunnel CRD, which was not operational anyway.
Only one field from MeshConfig was ever used, defaultConfig.proxyMetadata, the content
of which was written verbatim to the DaemonSet's environment variables. We'll be able to
set this field automatically once we introduce targetRef support, and until then,
should users require custom values, they can use ztunnel.env which has the same effect.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.50%. Comparing base (2c5951d) to head (cb36ce8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1236      +/-   ##
==========================================
+ Coverage   77.47%   77.50%   +0.03%     
==========================================
  Files          44       44              
  Lines        2823     2823              
==========================================
+ Hits         2187     2188       +1     
  Misses        527      527              
+ Partials      109      108       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[istio-testing]

In response to a cherrypick label: #1236 failed to apply on top of branch "release-1.27":

Applying: fix: remove MeshConfig from ZTunnel CRD
Using index info to reconstruct a base tree...
M	api/v1/zz_generated.deepcopy.go
M	bundle/manifests/sailoperator.io_ztunnels.yaml
M	chart/crds/sailoperator.io_ztunnels.yaml
M	docs/api-reference/sailoperator.io.md
Falling back to patching base and 3-way merge...
Auto-merging docs/api-reference/sailoperator.io.md
Auto-merging chart/crds/sailoperator.io_ztunnels.yaml
CONFLICT (content): Merge conflict in chart/crds/sailoperator.io_ztunnels.yaml
Auto-merging bundle/manifests/sailoperator.io_ztunnels.yaml
CONFLICT (content): Merge conflict in bundle/manifests/sailoperator.io_ztunnels.yaml
Auto-merging api/v1/zz_generated.deepcopy.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
Patch failed at 0001 fix: remove MeshConfig from ZTunnel CRD

[istio-testing]

In response to a cherrypick label: new issue created for failed cherrypick: #1237