feat: Make xDS Service name configurable via ENVOY_GATEWAY_SERVICE_NAME

[ADITYATIWARI342005]

What type of PR is this?

feat: New feature - adds configurability for Envoy Gateway service name

What this PR does / why we need it:

This PR makes the Envoy Gateway service name configurable through the ENVOY_GATEWAY_SERVICE_NAME environment variable, solving the issue where multiple gateway instances couldn't run in the same namespace due to hardcoded service name.

Usage:

env:
- name: ENVOY_GATEWAY_SERVICE_NAME
  value: "my-custom-gateway"

Which issue(s) this PR fixes:

Fixes #6997 Closes #6997

Release Notes: Yes

[codecov[bot]]

Codecov Report

:x: Patch coverage is 93.22034% with 12 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 71.17%. Comparing base (a478b74) to head (a7b05fb). :warning: Report is 236 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/xds/bootstrap/bootstrap.go	94.83%	8 Missing :warning:
internal/cmd/certgen.go	0.00%	1 Missing :warning:
internal/infrastructure/host/infra.go	0.00%	1 Missing :warning:
internal/infrastructure/host/proxy_infra.go	0.00%	1 Missing :warning:
internal/xds/runner/runner.go	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7049      +/-   ##
==========================================
+ Coverage   71.07%   71.17%   +0.09%     
==========================================
  Files         228      228              
  Lines       40691    40806     +115     
==========================================
+ Hits        28922    29044     +122     
+ Misses      10072    10070       -2     
+ Partials     1697     1692       -5     

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[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. Please feel free to give a status update now, ping for review, when it's ready. Thank you for your contributions!

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. Please feel free to give a status update now, ping for review, when it's ready. Thank you for your contributions!