Support URL CEL library

[pikachu0310]

Provide functionalities similar to Go's net/url using the grpc.federation.url library.

• impl url.parse
• impl URL functions
• impl Userinfo functions
• impl other functions
• add url.parse test
• add URL functions test
• add Userinfo functions test
• add other functions test
• write docs/cel/url.md

[shuheiktgw]

I left some comments, so PTAL 🙏

[pikachu0310]

I have addressed ktgw's review comments and resolved the conflicts. Please review it again.

[shuheiktgw]

I left some comments so PTAL 🙏

[shuheiktgw]

LGTM 🙆‍♂️

[github-actions]

Code Metrics Report

	main (e478944)	#244 (4e0c688)	+/-
Coverage	66.0%	66.3%	+0.3%
Code to Test Ratio	1:0.4	1:0.4	+0.0
Test Execution Time	7m55s	7m45s	-10s

Details

  |                     | main (e478944) | #244 (4e0c688) |  +/-  |
  |---------------------|----------------|----------------|-------|
+ | Coverage            |          66.0% |          66.3% | +0.3% |
  |   Files             |             75 |             76 |    +1 |
  |   Lines             |          12418 |          12557 |  +139 |
+ |   Covered           |           8192 |           8320 |  +128 |
+ | Code to Test Ratio  |          1:0.4 |          1:0.4 |  +0.0 |
  |   Code              |          38524 |          39019 |  +495 |
+ |   Test              |          13878 |          14665 |  +787 |
+ | Test Execution Time |          7m55s |          7m45s |  -10s |

Code coverage of files in pull request scope (100.0% → 93.0%)

Files	Coverage	+/-
grpc/federation/cel/lib.go	100.0%	0.0%
grpc/federation/cel/url.go	92.1%	+92.1%

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Reported by octocov

[utahta]

LGTM!