Pass custom CA to grpc dial option

[KrishnaIyer]

Summary

Pass custom CA to grpc dial option, reverting: b2b5d2c

Changes

• Pass custom CA to grpc dial option

Testing

Locally

Steps

1. Set a custom CA to the CLI

export TTN_LW_CA=./ca.pem

2. Test fetching a gateway.

Results

Before:

go run ./cmd/ttn-lw-cli gtw list
INFO	Telemetry is enabled. Check the documentation for more information on what is collected and how to disable it	{"documentation_url": "https://www.thethingsindustries.com/docs/reference/telemetry/cli"}
WARN	[core][Channel #1 SubChannel #2]grpc: addrConn.createTransport failed to connect to {Addr: "[::1]:8884", ServerName: "localhost:8884", }. Err: connection error: desc = "transport: authentication handshake failed: tls: failed to verify certificate: x509: “localhost” certificate is not trusted"
WARN	[core][Channel #1 SubChannel #2]grpc: addrConn.createTransport failed to connect to {Addr: "127.0.0.1:8884", ServerName: "localhost:8884", }. Err: connection error: desc = "transport: authentication handshake failed: tls: failed to verify certificate: x509: “localhost” certificate is not trusted"
WARN	Finished unary call	{"duration": 0.0924, "error": "error:unknown:unknown (connection error: desc = \"transport: authentication handshake failed: tls: failed to verify certificate: x509: “localhost” certificate is not trusted\")", "error_correlation_id": "f9413aaa5fbb43159868c2b607b0da4a", "grpc.method": "List", "grpc.service": "ttn.lorawan.v3.GatewayRegistry", "grpc_code": "Unavailable", "namespace": "grpc"}
error:unknown:unknown (connection error: desc = "transport: authentication handshake failed: tls: failed to verify certificate: x509: “localhost” certificate is not trusted")
    correlation_id=f9413aaa5fbb43159868c2b607b0da4a

After

go run ./cmd/ttn-lw-cli gtw list
INFO	Telemetry is enabled. Check the documentation for more information on what is collected and how to disable it	{"documentation_url": "https://www.thethingsindustries.com/docs/reference/telemetry/cli"}
[]
INFO	New patch version available	{"current": "3.32.1-dev", "docs_url": "https://www.thethingsindustries.com/docs/getting-started/upgrading/", "latest": "3.32.2"}

Regressions

This fixes a regression.

Notes for Reviewers

...

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• Testing: The steps/process to test this feature are clearly explained including testing for regressions.
• Infrastructure: If infrastructural changes (e.g., new RPC, configuration) are needed, a separate issue is created in the infrastructural repositories.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.