feat: Add support for apiEndpoint and deprecate serviceAddress client configuration option.

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/Firestore/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
0.29.1: Pulling from googleapis/artman
Digest: sha256:b2a73f4dda03ef8fcaa973e3ba26d0cf34091f6c22c70add663af325931aef4d
Status: Image is up to date for googleapis/artman:0.29.1
synthtool > Cloning googleapis.
synthtool > Running generator for google/firestore/artman_firestore_v1.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/php/google-cloud-firestore-v1.
synthtool > Running generator for google/firestore/artman_firestore.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/php/google-cloud-firestore-v1beta1.
synthtool > Replaced "'serviceAddress' =>" in src/V1beta1/Gapic/FirestoreGapicClient.php.
synthtool > Replaced "'serviceAddress' =>" in src/Admin/V1/Gapic/FirestoreAdminGapicClient.php.
synthtool > Replaced "'serviceAddress' =>" in src/V1/Gapic/FirestoreGapicClient.php.
synthtool > Replaced '@type string \\$serviceAddress' in src/V1beta1/Gapic/FirestoreGapicClient.php.
synthtool > Replaced '@type string \\$serviceAddress' in src/Admin/V1/Gapic/FirestoreAdminGapicClient.php.
synthtool > Replaced '@type string \\$serviceAddress' in src/V1/Gapic/FirestoreGapicClient.php.
synthtool > Replaced '\\$transportConfig, and any \\$serviceAddress' in src/V1beta1/Gapic/FirestoreGapicClient.php.
synthtool > Replaced '\\$transportConfig, and any \\$serviceAddress' in src/Admin/V1/Gapic/FirestoreAdminGapicClient.php.
synthtool > Replaced '\\$transportConfig, and any \\$serviceAddress' in src/V1/Gapic/FirestoreGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1beta1/Gapic/FirestoreGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1beta1/FirestoreClient.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/V1beta1/FirestoreClientTest.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/Gapic/FirestoreGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/Admin/V1/Gapic/FirestoreAdminGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/FirestoreClient.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/V1/FirestoreClientTest.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/Admin/V1/FirestoreAdminClientTest.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/System/Admin/V1/FirestoreAdminClientSmokeTest.php.
synthtool > Running generator for google/firestore/admin/artman_firestore_v1.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/php/google-cloud-firestore-admin-v1.
synthtool > Replaced 'Copyright \\d{4}' in src/Admin/V1/Gapic/FirestoreAdminGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/Admin/V1/FirestoreAdminGrpcClient.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/Admin/V1/FirestoreAdminClientTest.php.
synthtool > Replaced '@group admin' in tests/Unit/Admin/V1/FirestoreAdminClientTest.php.
synthtool > Cleaned up 1 temporary directories.
synthtool > Wrote metadata to synth.metadata.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@2a8a0c4). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master   #2211   +/-   ##
========================================
  Coverage          ?   92.6%           
  Complexity        ?    4451           
========================================
  Files             ?     307           
  Lines             ?   13271           
  Branches          ?       0           
========================================
  Hits              ?   12290           
  Misses            ?     981           
  Partials          ?       0

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@2a8a0c4). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master   #2211   +/-   ##
========================================
  Coverage          ?   92.6%           
  Complexity        ?    4451           
========================================
  Files             ?     307           
  Lines             ?   13271           
  Branches          ?       0           
========================================
  Hits              ?   12290           
  Misses            ?     981           
  Partials          ?       0

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2a8a0c4...8051816. Read the comment docs.

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